Determinants of International Purchasing Success: An Analysis of the Status Quo of Research

International purchasing is one of the most important strategic topics for managers, and attracts more and more interest among researchers. The literature review in this article analyzes the status quo of theoretical knowledge and empirical research in international purchasing. We find that, owing to the relatively recent focus on international purchasing as a scientific field, research often still lacks strong theoretical foundations, does not make enough use of advanced empirical methods, and still lacks systematic insights on the intricacies of purchasing success. Building on what progress has been made in past studies, we provide a strategy and structure framework of determinants of international purchasing success that seeks to contribute to clearer theoretical thinking in the discipline and offers a formidable platform for the design of future empirical research.

The Selection of Papers
As we are interested in further analyzing international purchasing questions, we systematically reviewed the abovementioned set of 14 journals. We screened all issues in the seven-year period between 2006 and 2012 (i.e. the period tying in with the analysis period of Quintens et al. (2006b)) and considered articles that focus on cross-border purchasing at the level of industry, firm, or business unit, and that work on this issue as a central subject. In addition to this screening, we consulted the EBSCO database using a keyword search referring to the search terms global, international, foreign, offshore, inward, and worldwide, in combination with purchasing, sourcing, procurement, and import. Finally, we excluded papers that consider consumer buying behavior and those that so not seek to contribute to the development of international purchasing theory. This approach resulted in 36 relevant articles. We also used a snowball approach based on the literature list of previously identified papers, which led us to identify three further papers on this matter. In sum, 39 papers were found, with the overwhelming majority coming from the SCM field (

Theoretical Foundations in Purchasing and Supply Chain Management
Owing to the multidisciplinarity of purchasing and supply chain management (P&SCM), there is no one accepted research paradigm to explain aspects of purchasing research; many theories are referred to, including international trade, foreign direct investment, offshore production, product life cycle, and manufacturing theory (Swamidass, 1993). In spite of the variety of theories used, Harland et al. (2006) conclude that there is still a lack of theory in the field, and that purchasing and even SCM as a scientific discipline are still in its infancy (see also Quintens et al., 2006b). The more optimistic view on the situation is that of Chicksand, Watson, Walker, Radnor, and Johnston, who hold that "although a young discipline, P&SCM is also a relatively rich one" (Chicksand et al., 2012: 458). Chicksand et al. (2012) found that only one-third of the (1,113 P&SCM) articles they reviewed have a theoretical foundation. There is also no visible trend to more theory use over time, even if those theory-based papers achieve a higher number of citations. Defee, Williams, Randall, and Thomas (2010) found that 364 articles published in five important supply management journals between 2004 and 2009(Note 1) used more than 180 different theoretical approaches to explain logistics and SCM issues. Considering only articles on purchasing research, they conclude that approximately 30% used microeconomic theory (containing, for instance, transaction cost economies, resource dependence theory, and principal-agent theory), followed by competitive theory (16%, including approaches such as the resource-based view, the contingency approach, the knowledge-based view, dynamic capabilities, and cluster theory), systems theory (15%), and social exchange theory (10%).(Note 2) In their literature review on purchasing organizations, Glock and Hochrein (2011) identified only eight theory-based papers out of 85 articles. Pagano's literature review on the organization of international sourcing activities, published in 2009, completely waives an analysis of the applied theoretical underpinnings. Quintens et al. (2006b) did not analyze the particular theoretical foundations used for the 123 international purchasing articles they reviewed, but conclude that "it is time now to focus on a business paradigms and theories of the firm, which have to be translated into a global purchasing logic" (Quintens et al., 2006b: 175).
In our literature review, which covers 2006 to 2012, the most prominent theories applied were competitive approaches (16 papers), followed by microeconomic and systems theories (five articles each). In the first group, the most cited theories are the resource-based view, including dynamic capabilities. The resource-based view is used to explain the possibility of transferring resources, such as knowledge or technology, from external suppliers to the firm -for instance, by establishing close supplier partnerships -and thus gaining or enhancing a competitive advantage (Shook, Adams, Ketchen, & Craighead, 2009). Seven of the analyzed papers use the resource-based view, especially when dealing with international purchasing management matters (e.g. Gonzalez-Padron et al., 2008;Quintens et al., 2006a;). Five articles are based on a contingency approach, focusing on the fit between a firm's organization and its environment (Glock & Hochrein, 2011). For instance, the authors apply the contingency approach to examine the relationships between organizational culture, learning, entrepreneurial innovation, and purchasing outcomes in different ethical climates . Furthermore, a small number of publications is based on a cluster approach that mostly deals with the advantages and disadvantages of having local or global suppliers (e.g. (Steinle & Schiele, 2008)). To explain the firm's advantages by reducing sourcing costs or revealing better sourcing markets, authors make use of comparative or competitive advantage models Ruamsook et al., 2007). The transaction cost approach, which is dominant in microeconomic theories, focuses on a reduction of transaction costs when sourcing abroad (Shook et al., 2009). It is referred to by the authors of four articles to explain the sourcing activities of Western companies in Asia (e.g. Wang et al., 2011; Giannakis et al., 2012). Among systems theories, network theory is most prominent. Network theory draws on the firm's advantages, which are generated from being a central part of a supplier network and which improve the firm's purchasing performance. Four of our analyzed articles are based on network theory, especially when dealing with supplier management topics (e.g. Hultman et al., 2012;Tunisini & Bocconcelli, 2009). Besides these most common theories, several authors apply other approaches to explain international sourcing phenomena such as grounded theory, inventory, or social capital theory, fuzzy set theory, or resource dependence theory (e.g. Agndal, 2006;Weber et al., 2010;Carter et al., 2008;Chan et al., 2008;Gelderman & Semeijn, 2006, Manuj & Mentzer, 2008Tsai et al., 2009;Young et al., 2009). We also find an increased usage of "intellectual eclectic" approaches (i.e. combining different, generally incompatible theoretical approaches), which was also highlighted in the review by Chicksand et al. (2012). Nine articles completely lack a clear, strong theoretical foundation (e.g. Kotabe et al., 2008;Maltz et al., 2011;Millington et al., 2006;Knudsen & Servais, 2007). Although scholars mention one of the above popular theoretical approaches, they seem to not link their own research to this theory well (Chicksand et al., 2012;Defee et al., 2010). In sum, also after 2005, there is no major focus visible on single theories, and the use of business paradigms, as called for by Quintens et al. (2006b), is still scarce. literature reviews are categorized in the last group -conceptual research papers. While the number of conceptual papers is low, the overwhelming majority (33 of 39) makes use of empirical research methods. Nearly half of all papers still rely on qualitative methods, whereof 10 focus solely on case studies (mostly based on interviews and secondary data) (e.g. Fredriksson & Jonsson, 2009;Reuter et al., 2010;Young et al., 2009;Trautmann et al., 2009). Three papers use mixed methods by combining case study and/or workshop insights with survey results (e.g. Mohamad et al., 2009). The other half relies on quantitative methods referring to quantitative survey data.

Figure 1. Overview of Research Methodologies in International Purchasing Research
All authors base their survey on a literature review; few make use of a qualitative pre-survey (e.g. Maltz et al., 2011;Ogden et al., 2007;Kusaba et al., 2011). As noted by Quintens et al. (2006b), factor analysis still is one of the most popular methods. Six out of 10 articles that provide information on the method used apply confirmatory factor analysis (e.g. Tsai et al., 2009;Kusaba et al., 2011;Sinkovics et al., 2011). Other methods are rarely used (such as perceptual mapping by Carter, Maltz, Maltz, Goh, and Yan (2010) and Maltz et al. (2011), gap analysis (Mohamad et al., 2009), or analysis of variance (Knudsen & Servais, 2007)). Only one study is based on a multiple linear regression procedure . In sum, there is a shift to more quantitative studies in global sourcing research and the quantitative analyses techniques toolset is slightly increasing. The balanced use of quantitative as well as qualitative methods (or a combination) and the more precise description of the methods' applications shows that research designs and data analysis procedures are becoming more important elements of global sourcing research. However, more advanced quantitative methods, such as multiple regression analyses or even structural equation modeling (SEM) techniques, have to our best knowledge not yet been applied.
In researching the determinants of international purchasing success, multivariate analyses procedures, which are able to explore and test theoretical causal relationships, are valuable, because they provide information on the importance of individual strategy and structure determinants for company performance. In particular, SEM techniques present a promising statistical route, because they enable the simultaneous exploration of causal relationships between various independent (e.g. dimensions of strategy and structure) and various dependent (e.g. performance in terms of time, cost and quality) variables in one research model. For a relatively new theoretical field, where strong theory is lacking and authors are still in the process of theorizing, especially partial least-squares SEM is the method of choice (see Hair, Hult, Ringle, & Sarstedt, 2014;Hair, Sarstedt, Ringle, & Mena, 2012).

Research Streams Identified in Past Reviews
Past literature reviews identify three primary research streams that are of special interest to scholars in international sourcing: process models, management and organizational designs, and motives or drivers of international purchasing (see the overviews by , Hultman et al. (2012), and Quintens et al. (2006b)). In addition, Quintens et al. (2006b) introduce consequences of global purchasing as a fourth study category. Process models focus on describing the process of incrementally gaining experience in international sourcing. The most influential model is advanced by Monczka & Trent, 1991, 2002, 2005, who define five stages of development: (1) domestic purchasing only, (2) international purchasing based on need, (3) international purchasing as part of a sourcing strategy, (4) integration and coordination of international sourcing strategies across worldwide buying locations, and (5) integration and coordination of international sourcing strategies with other functional groups. Process frameworks are still common today and are, for instance, used in order to analyze the differences in the perception of success drivers at different stages of international purchasing (e.g. Mohamad et al., 2009), and for analyzing the development of supplier relationships (e.g. Hultman et al., 2012;Knudsen & Servais, 2007).
The second research stream pays particular attention to the management of international sourcing activities and the related organizational designs (see the overviews in  as well as Hultman et al. (2012)): Between 2006 and 2012, 20 publications address either strategy or structure, or individual aspects of both categories simultaneously (this is most common). Authors often discuss topics such as appropriate risk management approaches (e.g. Christopher et al., 2011), international sourcing strategies in general (e.g. Quintens et al., 2006a;Gelderman & Semeijn, 2006), aspects of supplier selection and management (e.g. Carter et al., 2008;Chan et al., 2008;Millington et al., 2006;Sinkovics et al., 2011), location choice criteria (e.g. Maltz et al., 2011;Deane et al., 2009), and optimal product characteristics for international sourcing (e.g. . While studies that focus on organizational topics involve research that bundles a variety of organizational variables (e.g. Kusaba et al., 2011), a focus on single organizational aspects (e.g. Trautmann et al., 2009) is more common.
A third group of studies looks at the drivers (i.e. elements that favor the decision for international sourcing), facilitators (i.e. conditions that ease the implementation of international sourcing) and barriers (i.e. factors that aggravate the pursuit of international purchasing) to international sourcing. While past research has established comprehensive collections of potential drivers, facilitators, and barriers (see the overviews by Nassimbeni (2006) Giannakis et al., 2012); what is more common is a focus on cost effects (e.g. Fredriksson & Jonsson, 2009;Young et al., 2009;Weber et al., 2010), effectiveness (e.g. Hartmann, Bals, & Kaiser, 2008;Trautmann et al., 2009), and profitability (e.g. Kotabe et al., 2008;. Supplier-relationship-related performance measures, such as responsiveness (e.g. Sinkovics et al., 2011), or sustainability  are also found. There is a clear research gap concerning the performance outcomes and on aligning these outcomes with the fundamental strategy and structure choices in international sourcing.

A Strategy and Structure Framework
We will develop a different framework in order to guide the review's content analysis. We will develop a classification of the success determinants guided by theory that offers mutually exclusive and independent (to analyze) categories defined to cover all issues addressed by the review (e.g. Glock and Hochrein (2011), based on Holsti (1969)). We will conceptualize these determinants into the strategy and structure characteristics that are supposed to affect company performance.
Regarding the organization and design of the international purchasing activities, we will build on the work of Glock and Hochrein (2011). To assess the performance of alternative structural designs, the authors refer to the contingency and configuration approaches as theoretical foundations. Both approaches focus on the interplay of the organization's environment and its structure. The basic idea is that organizations perform better when their structure is properly aligned with the environmental or contextual conditions (Child, 1972), and thus that the appropriate structure positively affects performance. Glock and Hochrein (2011), who focus on the alignment of structure, identify the following six important elements of purchasing organization structure: (1) (De-)centralization refers to the concentration or aggregation of decision-making authority in a single organizational unit, for instance at the headquarters level.
(2) Configuration is determined by the design of the authority structure in the organization; it involves aspects such as vertical and lateral spans of control, criteria for segmentation, and numbers of positions in various segments.
(3) Involvement includes lateral involvement, i.e. the number of departments, divisions, or functions that participate in the sourcing decision, and vertical involvement, i.e. number of hierarchical levels involved, as well as the size of the buying center in terms of the number of people involved in the purchasing process. (4) Specialization refers to the way labor is divided win the organization, for instance, either by tasks or functions. (5) Standardization is the extent to which activities are precisely defined. (6) Formalization describes the extent to which an organization relies on rules and procedures to direct the behavior of its members, for instance, the definition of rules that regulate decision-making processes (see (Glock & Hochrein, 2011)). One important success factor not explicitly included in the classification by Glock and Hochrein (2011), but analyzed by several authors (e.g. ; ; ) is the positive impact of top management commitment, which can ensure the availability of the necessary resources, such as personnel, time, and budget. This ensures that the strategic focus becomes visible for all employees involved in the purchasing process, and that international sourcing activities become realizable. We will incorporate the aspect of commitment into the category involvement.
The contextual or environmental factors identified by Glock and Hochrein (2011) can to some extent be influenced by a company's strategic choices. For instance, if a company chooses to operate in a certain country, this country's environment is realized by this location choice: "…the business environment is also 'selected' when it [the firm] decides to source parts from that supplier…" (Deane et al., 2009, p. 865). Hence, it is not only about creating a fit between structure and a non-influenceable environment, but to appropriately influence contextual factors by making the right strategic choices. In further conceptualizing strategic options from a sourcing perspective, we will basically follow the approach of Arnold (2002), who identifies the following four relevant sourcing strategy elements which, together, are supposed to form the overall purchasing strategy: (1) supplier management (e.g. single, dual vs. multiple sourcing); (2) sourcing object strategy (e.g. product characteristics), (3) location strategy, (e.g. regional vs. global or specific market, such as emerging market, sourcing strategies); (4) time strategy, (e.g. on stock, demand tailored, and just-in-time strategies) (Arnold, 2002).
In explaining why and how these strategic choices affect performance, the following theoretical streams can be consulted: Steinle and Schiele (2008) refer to the cluster approach and the resource-based view (RBV). According to the cluster approach, a company can profit from being part of a cluster that provides firms along a value chain with competitive advantages and thus with higher performance or profitability (Porter, 1990). In terms of sourcing, this relates for instance to supplier management in terms of searching suppliers located in a certain local cluster (location strategy). According to the RBV, a firm gains competitive advantages owing to its superior internal resources.
Although not incorporated in its pure form (Barney, 1991;Wernerfelt, 1984), several theoretical extensions have been proposed that view the interfirm relationship between the buyer and supplier as part of the company's resources. For instance, there has been a lively discussion of relational competencies anchored in a company's network (e.g. Duschek, 1998;Dyer & Singh, 1998;Mildenberger, 2001) and the extended enterprise (Dyer, 2000;Harland, 1997;Kinder, 2003). Both approaches suppose that an organization can derive a competitive advantage from its relationship to partners, in the form of horizontal alliance partners or vertical supply chain partners. Hence, as argued by Steinle and Schiele (2008), suppliers can be company-addressable resources and can contribute to a sustainable competitive advantage ( (Barney, 1991); Steinle, 2005;Steinle & Schiele, 2008) and thus to performance. Theoretical arguments on sourcing object strategy are mainly found in transaction cost approaches, which focus on all facets on the continuum between the make or buy decision. Any sourcing decision involves an evaluation of costs incurred from internally (producing) providing a product vs. purchasing it from an external source (market) (Williamson, 1975(Williamson, , 1979. According to transaction cost approaches, an appropriate sourcing object strategy will reduce costs and therewith increase performance. These approaches also focus on the product characteristics in terms of specificity, uncertainty, and costs in relation to the global sourcing success. Finally, the impact of time strategy on performance and the questions of an ideal sourcing rhythm and lot size have long been in the focus of theorists (see for instance the approaches derived by Harris (1915) and Andler (1929)).

Strategy Determinants of Global Purchasing Success
The papers analyzed can be classified along both the three research streams identified in past reviews as well as the new strategy and structure framework we derived (see Table 2).
According to our literature review, the majority of authors analyze questions of supplier management (see Table 2) when it comes to strategy determinants of global purchasing success. In supplier management, authors mostly concentrate on questions of supplier selection (e.g. , Deane et al., 2009 and the management of supplier relationships (e.g. Christopher et al., 2011;Giannakis et al., 2012;Knudsen & Servais, 2007;Millington et al., 2006). Chan et al. (2008) find that the most important criteria for choosing the right suppliers are costs (e.g. logistics management costs, tariffs), supplier quality in terms of capabilities, the delivered product and service, and risk factors such as political stability. The latter -the analysis of global supply chain risks -is addressed by Deane et al. (2009), who propose a complementary supplier selection model in light of mitigating regional risks associated with suppliers' locations and density risks associated with the geographic proximity of the chosen suppliers. International sourcing risks and mitigation strategies are also addressed by Christopher et al. (2011), who identify the major (supply, environmental, process, control, and demand) risks in international sourcing for different industries. For instance, in FMCG, transport risks, a high dependency on low-cost sourcing in combination with a perceived loss of control and corporate social responsibility issues are identified as the major risks. Based on case studies, the authors identify four generic strategies to address such risks (network re-engineering, collaboration, agility, and a risk management culture), including close collaboration between parties involving trust and information transparency. Trust, effective communication, and stable relationships are also among the top mitigation strategies listed by Wang et al. (2011). Overall, the relationship with suppliers either in terms of cooperation modes (governance structures) and relationship characteristics (e.g. trust) is prominent in past research (e.g. Giannakis et al., 2012;Knudsen & Servais, 2007;Millington et al., 2006;Fredriksson & Jonsson, 2009;Mohamad et al., 2009; also list relationship quality and focus on the moderating effects of ethical climate, while Reuter et al. (2010) analyze how sustainability issues are incorporated into the buyer-supplier relationship).
Our understanding of supplier strategy concentrates on the number of suppliers in terms of single sourcing vs. multiple sourcing. Gelderman and Semeijn (2006), who refer to this as purchasing portfolio management, introduce a purchasing portfolio matrix characterized by the number of suppliers (small to large) and the value of the purchase (low to high), and formulate four purchasing strategies based on the resulting quadrants: bottleneck sourcing in the case of a small number of suppliers and a low purchase value; strategic (partnership) sourcing for few suppliers with a high purchase value; noncritical sourcing for low-value purchases from multiple suppliers (with standardized procedures); and leverage, i.e. monitoring and managing supplier performance, for high-value purchases from multiple suppliers. Similarly, Steinle and Schiele (2008) argue that becoming a preferred customer to strategic suppliers is key in international strategic sourcing.
The high number of papers focusing on international supplier relationship management leads to the assumption that supplier management has an important impact on the international purchasing performance.
Furthermore, strategic options regarding the sourcing object and location are popular (e.g. ; ). The sourcing object is issued in two different ways. The major group of authors discusses the product's optimal characteristics in order to source it successfully in the global market Quintens et al., 2006a;Steinle & Schiele, 2008;Trautmann et al., 2009;Gelderman & Semeijn, 2006). These characteristics are described in different terms, for instance, regarding a product's specificity, technology, criticality/uncertainty, and costs. Gelderman and Semeijn (2006) consider the value of purchases as the crucial variable. A second group of authors refer to the final product, or specifically to its quality, innovation, or delivery as a result of a sourcing decision and finally as a purchasing performance measure Ruamsook, Russell, & Thomchick, 2009;Wang et al., 2011). Location selection criteria are considered by several authors. Fredriksson and Jonsson (2009) group factors into the categories infrastructure, culture, human capital, and policies and regulations, and derive consequences and performance effects from these dimensions. For instance, in their case study of European and Chinese business relationships, they describe communication difficulties relating to varying cultural backgrounds. These involve a low quality of information exchange, which leads to a decreasing product quality or flexibility. Kamann and van Nieulande (2010) also offer different categories that influence country selection: costs (e.g. wages, customs, tariffs), competence (e.g. industrial performance, education, and training, innovation), quality (ISO ownership ratio), logistics (e.g. lead time, time to export, and infrastructure), and a list of other factors (e.g. intellectual property protection, institutions, macroeconomic stability, technology readiness, corporate responsibility issues such as the use of child labor, safety and pollution, and foreign exchange risks). In contrast, Carter et al. (2008), Maltz et al. (2011), and waive categorizing the influencing factors and provide a loose collection of single elements that impact the sourcing country decision, considering for instance labor costs, local market attractiveness, work ethics, delivery, and the political environment. Tsai et al. (2009) include only single factors -cultural differences and regulations -in their study on global responsiveness.
Timing aspects are not frequently researched. In the context of time strategy, Christopher et al. (2011) identify supply chain agility (i.e. the ability to respond swiftly to unpredictable variations in demand or supply) as one of the best practice strategies in global sourcing. (Fredriksson & Jonsson, 2009) distinguish between a short and a long supply chain of casting goods and draw interferences for China; for instance, they find that quality problems and long lead times make it necessary to maintain safety stocks. Finally, Ruamsook et al. (2009) refer to timing aspects, namely on-time receipt, cycle-time consistency and length as performance outcomes of international sourcing. Table  3 lists the authors who are active in each of the above strategy categories.
In contrast to the literature review of Glock and Hochrein (2011), we count more articles that consider aspects of involvement, i.e. the number of players and hierarchical levels participating in sourcing decisions than (de-)centralization (see the overview in Table 4). Authors mostly focus on the effects of involving suppliers and building close relationships Mohamad et al., 2009;Quintens et al., 2006b;Sinkovics et al., 2011), and supply networks Hultman et al., 2012) on different purchasing performance levels. Other researchers discuss aspects of purchasing team composition (Manuj & Mentzer, 2008); ), for instance, regarding its effect on the quality of early risk identification (Manuj & Mentzer, 2008), or on purchasing's learning orientation . Even if this is not central to the analyzed articles, executive support as a critical factor of global purchasing success is mentioned several times Kusaba et al., 2011;Mohamad et al., 2009;Weber et al., 2010). Glock and Hochrein (2011) defined specialization as the division of labor in an organization and as task repetitiveness levels; none of the papers we reviewed incorporate specialization as such. Instead, authors refer to specialization in the context of capabilities, skills, and knowledge. The most prominent aspects are the need for personnel skills, knowledge, and abilities in relation to successfully sourcing abroad Mohamad et al., 2009;Fredriksson & Jonsson, 2009;Kusaba et al., 2011;Quintens et al., 2006b;Wang et al., 2011;. A few authors focus on the skills needed for sourcing in special regions or countries, for instance low-cost countries, or China in particular ( ; (Fredriksson & Jonsson, 2009); ; ). These articles emphasize the importance of certain skills or competencies such as an understanding and interest in culture. Further papers have a more general view of the role of expertise concerning performance measures, such as , who examine the role of dynamic capabilities on supplier evaluation and development and, finally, in achieving competitive advantage, or , who research the dominance of headquarters in organizations owing to a lack of expertise in subsidiaries. The impact of developing skills in terms of organizational learning on purchasing outcomes is also discussed .
Originally closely related to specialization is configuration, i.e. authority structures, segmentation criteria, and the number of positions in various segments enabling skills building in terms of business functions or objects. Only a few authors consider the impact of configuration aspects on international sourcing topics, such as different types of configuration or special logistics solutions types between producers and retailers . Mohamad et al. (2009) focus on the hierarchical position of the purchasing department and therewith the access to better opportunities to attain resources needed.
Based on our literature review, we find that especially standardization has seen attention in recent years, either regarding sourcing a standardized product that can be critical to success, for instance, if sourcing from China Fredriksson & Jonsson, 2009;, or regarding the standardization of purchasing processes, the latter being the more prominent category. In doing so, authors investigate a variety of different aspects, for instance, process standardization of supplier selection, evaluation, and development (e.g. ; Kusaba et al., 2011;Reuter et al., 2010;Bygballe et al., 2012;Giannakis et al., 2012), decision-making guidelines for country selection Carter et al., 2008), or the availability and form of required information and IT integration ; Mohamad et al., 2009;Sinkovics et al., 2011;Kotabe et al., 2008). Articles also deal with the importance of a more precise planning when sourcing abroad Wang et al., 2011;Young et al., 2009;Giannakis et al., 2012;, systematic performance tracking ; ), and risk management (Manuj & Mentzer, 2008;Tsai et al., 2009;Christopher et al., 2011), and the need for precise sourcing cost analysis Weber et al., 2010).
Matters of formalization have received less attention in recent years. Only four articles directly consider the role of formalization in the purchasing context ; ; ; ). For instance, Gonzalez-Padron et al. (2008) test if autonomy and therewith the absence of formalization in the purchasing process has a positive impact on organizational learning and innovation as well as on the participant's relationship quality and the sourcing process' cycle time.  seek to find out whether there is an optimal degree of formalization when sourcing internationally.
This overview on the use of structural dimensions in the context of international purchasing articles reveals some interesting insights: the number of papers focusing in centralization aspects is much lower as expected after the study by Glock and Hochrein (2011). In contrast, involvement and specialization play an important role and the by far most prominent organizational dimension is standardization.

International Purchasing Success
Ultimately, these strategy and structure options are the determinants of increased performance, which is the major target variable of all sourcing activities. The content analysis of the papers shows that there is much valuable research in each of the strategy and structure categories. However, no author addresses the overall set of identified strategy and structure elements, which means that the comparative importance of the individual elements cannot be evaluated.
According to Murray, Kotabe, & Wildt, 1995), performance be interpreted as strategic (e.g. measured as market share) and financial performance (e.g. return on sales). Previous studies showed that direct retrieval of performance data is not useful owing to the very small respondent group. Therefore, Murray et al. (1995) used these performance indicators in relation to the three largest competitors. They rely on Dawes (1999), who states that there is a high correlation between the respondent's subjective performance perception in relation to the competitors and objective performance. Yet, if international sourcing really leads to an increased economic performance is poorly proved (Gelderman and Semeijn, 2006;Bygballe et al., 2012). The effect of international sourcing on overall firm performance is usually blurred by the variety of its determinants and therewith sometimes hard to measure. International sourcing performance should therefore be considered separately.
In current research papers, this performance measurement often lacks a clear operationalization. Articles that concentrate on other (non-globally) strategic sourcing aspects and their effects on sourcing performance often work on one of the facets involved in the triangle of cost, quality, and time factors (including flexibility and delivery time) (e.g. Carter, Monczka, & Mosconi, 2005;Krause, Pagell, & Curkovic, 2001;González-Benito, 2007. Of the reviewed papers, only Giannakis et al. (2012), based on Chen and Paulraj (2004), and Ruamsook et al. (2007) use this full classification of performance. We would therefore appreciate a stronger focus on multidimensional sourcing performance measures in future research.

Conclusion and Future Research Directions
Building on former literature reviews, we updated the status quo of theory and research in international purchasing by screening the relevant literature and analyzing 39 found papers. We find that, while much progress has been made in the field, theoretical implications and essential insights for practitioners are still lacking.
Authors have identified a lack of structured theory-testing and theory-building in global purchasing research. Current literature reviews on purchasing and supply chain management report that only 10% to 30% of reviewed articles have a theoretical foundation (Chicksand et al., 2012;Glock & Hochrein, 2011). In our review of the literature, 66% of papers refer to a theory and establish a theoretical foundation for their research objective. Hence, in contrast to others, our analysis points to an upward trend in terms of theory use over time. Nonetheless, 34% of studies do not relate to theory at all or insufficiently link theoretical thinking to their research designs. Where theory is used, the most prominent theories applied derive from competitive approaches (41%), followed by microeconomic and systems theories (13% each). This corresponds approximately to the shares of dominant theories used, as identified in other literature reviews from supply chain management . However, we cannot identify a true focus on any single theory to be applied to global sourcing studies; the use of business paradigms, as called for by Quintens et al. (2006b), is still scarce. The situation can be characterized by various theoretical streams: Most cited is the resource-based view, including dynamic capabilities, followed by the contingency and cluster approaches. Other prominent theories are transaction cost and network thinking. A further trend that has evolved is that many authors follow an intellectually eclectic approach (Chicksand et al., 2012). Still, our review leads us to conclude that theoretical underpinnings are not satisfactorily applied to empirical research.
Empirical research designs have in the past few years shifted towards more quantitative approaches, and data analysis procedures are becoming more important elements of global sourcing research. Yet these designs do not make use of the full potential offered by modern research procedures. Factor analysis still is the most popular tool, while techniques such as regression analysis and structural equation modeling, which are common in other disciplines, are rarely or never used. However, these more advanced multivariate procedures would enable insights into the complex causal relationships between different facets of global purchasing and global purchasing success.
In terms of research content, former literature reviews outlined three major streams: research on process models, on management and organizational designs, and on motives or drivers of international purchasing. While process models are not often found in the reviewed period, most published papers do study management and organizational designs. This is a promising route, in light of identifying norm strategies to purchasing success. However, future research urgently needs to increase the systematic application and testing of different theoretical streams to purchasing performance in order to contribute to theory-building or to the identification of theories that best apply to the challenges of global sourcing. While more studies are analyzing the performance outcomes of different purchasing decisions, few concentrate on this research question. To disentangle the determinants of purchasing success, studies are needed that systematically analyze the major strategy and structure options that managers can pursue in order to enhance performance.
Our study contributes to this field by developing a framework of the basic strategy and structure dimensions to be incorporated into a research approach that focuses on international purchasing success. In terms of strategy, these are supplier management, sourcing object strategy, location, and time strategy. Regarding structure, aspects of (de-)centralization, configuration, involvement, specialization, standardization, and formalization are the key elements. All these dimensions are represented in the analyzed articles; specialized insights into these single aspects are often provided. Lately, supplier management was the most prominent topic of the strategy dimension, with 44% of articles offering implications on successful supplier management strategies in an international sourcing environment. In contrast, timing strategy is a neglected aspect (8% of studies). In sum, the extent of supplier management topics in relation to topics of other purchasing strategy dimensions is much higher. This can be seen as expression of higher researcher interest and managerial relevance. Nevertheless, it is questionable, if location choice, object, and timing topics really have a lower influence of international purchasing performance. Regarding the structure determinants, most articles (54%) we reviewed deal with standardization aspects, followed by involvement (31%) and specialization (28%). Considering the high research interest, these dimensions can be considered as most influential organizational dimensions on international purchasing performance. The latter three structure aspects -(de-)centralization, formalization, and configuration -play a fairly minor role in current research: Not more than 13% of papers look at these elements. This is in strong contradiction to the use of structural variables in research on purchasing organizations identified by Glock and Hochrein (2011), who reported the highest interest in aspects of (de-)centralization, formalization, and involvement. Due to a lack of a simultaneous examination either of all organizational determinants, or the strategy dimensions, or both, it remains unclear, if the importance and influence on purchasing performance of less considered aspects is really as low as assumed here.
Two important conclusions need to be highlighted from our content analysis: First, even if many articles consider more than one of the presented determinants, a comprehensive approach of all strategy and structure variables is still missing. Second, articles are often very specific in nature. For instance, the papers on supplier management mostly do not investigate the overall supplier management options. In contrast, they focus on individual aspects in the supplier management process, such as supplier selection, evaluation, or supplier (relationship) development.
The implications for future research evolving from the insights gained herein are: First, we encourage authors to make use of the theory-driven framework of strategy and structure determinants of global purchasing. This will lead to a more structured view on the strategic option, a purchasing department is faced to when sourcing internationally. Besides advantages for theory development, this approach allows deriving more profound managerial recommendations. Second, we identify the need to apply more advanced multivariate analysis procedures in global purchasing research that are able to explore and test multiple theoretical causal relationships. Third, authors are encouraged to test more comprehensive theoretical models of the strategy and structure determinants of purchasing performance. Fourth, there is a need to research the impact on specific facets of purchasing success -here we call for the simultaneous incorporation of time, cost, and quality aspects of purchasing performance -in addition to drawing implications for the overall performance outcomes. These might be important steps toward leading international purchasing research in a direction of focusing on actually relevant topics, as well as toward theory-building and maturing purchasing & supply chain research as a scientific discipline.


CCI CANCELLATION USING KF IN FADED MIMO CHANNELS

Multi input multi output system (MIMO) has become a viable option to meet the demand of high data rate wireless communication. But MIMO system performance is severely affected by the presence of co-channel interference (CCI). CCI cancellation in MIMO channel therefore is a challenging area of research. This paper provides a Kalman Filter based CCI cancellation approach. In the severely faded Rayleigh channel in coded MIMO set-up, experimental results show that Kalman filter based approach for CCI cancellation provides satisfactory results and can thus prove to be a reliable CCI cancellation technique in future. KeywordsCo-channel interference, MIMO, STBC, Rayleigh Fading

I. INTRODUCTION
In recent years, researchers have found that substantial amount of performance gain of transmitted and receive diversity can be achieved by using multiple antennas. Multiple-Input Multiple-Output (MIMO) system. MIMO technology is a part of many high data rate wireless communication systems. It increases capacity and performance of wireless links. This is generated by the transmitreceive diversity inherent in MIMO technology. Space-time block code (STBC) is a method usually employed into MIMO wireless communication systems to improve the reliability of data transmission using multiple antennas. The use of STBC with diversity gains derived from MIMO setup provide improved performance in faded wireless channels.
Co-channel interference (CCI) in wireless channel is a degrading phenomenon. It is more so with MIMO systems and the capacity of such systems is limited considerably by the presence of CCI. Therefore, CCI cancellation is challenging area and continues to attract research. The receiver design which could effectively remove the CCI and give a satisfactory receiver performance is a pertinent problem.
Many methods of CCI cancellation in MIMO domain have been proposed. In paper [2], STBC is used to combat CCI. A minimum mean square error (MMSE) and maximum a-posteriori (MAP) receiver design was proposed in [3]. In [6], maximum likelihood (ML) estimate of channel using training sequence are studied assuming temporally and spatially white noise.
In the present work, we study channel estimation and data detection of coded MIMO system with two CCI sources under fading in an interference limited environment using recursive Kalman Filter (KF). We specially use an application specific KF for a coded -MIMO set-up which cancels CCI successfully. The paper is organised as follows. Section II introduces basic theoretical notions regarding the model. Section III describes the system Model. Experimental details and stimulated results are included in Section IV. Section V contains the conclusion of the work.

II. BASIC THEORTICAL NOTIONS
The use of STBC and MIMO has proven to be an effective combination. This section provides a brief description of STBC, CCI, Rayleigh fading and related channel aspects considered for the work.
A .Rayleigh Multipath Fading Channel-The propagation environment for any wireless channel is either indoor or outdoor may be subject to LOS (Line-of-Sight) or Non LOS (NLOS). A probability density function of the signal received in the LOS environment follows the Rician distribution, while that in the NLOS environment follows the Rayleigh distribution. In mobile radio channels, Rayleigh distribution is commonly used to describe the statistical time varying nature of the received envelope of a flat fading signal or the envelope of an individual multipath component [1].

B. Space-Time Block Code (STBC)-
In general multiple antennas are used to achieve spatial diversity and to achieve time diversity the transmission is repeated n times. Scope of diversity is expanded by using multiple antennas at both the receiver and transmitter. The capacity of multi-antenna systems far exceeds that of a single antenna system and capacity grows at least linearly with the number of transmit antennas as long as number of received antenna is greater than or equal to number of transmit antennas. STC were first introduced by Vahid Tarokh, Nambi Seshadri and Robert Calderbank from AT&T research labs in 1998 as a novel means of providing transmit diversity for the multiple antennas fading channel. These STCs achieve significant error rate improvements over single-antenna systems. Their original scheme was based on trellis codes but the simpler block codes were utilised by Siavash Alamouti [14], and later Vahid Tarokh, Hamid Jafarkhani and Robert Calderbank [15] to develop STBCs. STC involves the transmission of multiple redundant copies of data to compensate for fading and thermal noise in the hope that some of them may arrive at the receiver in a better state than others C. Co-channel interference (CCI)-MIMO architectures are useful for combined transmit receive diversity. For its parallel mode of transmission, MIMO system offer high data rate in narrow bandwidth .MIMO system is characterized by multiple antenna elements at the transmitter and receiver, have demonstrated the potential for increased capacity in rich multipath environments. A MIMO system input-output relationship can be written as ..,N denoting the transfer function between the jth transmit and ith receive antenna respectively. Propagation related variations modeled by Rayleigh, ITU pedestrian and vehicular channels and Rician distribution can be included in matrix H.

Fig1: A generic MIMO scheme with interferer
Considering the presence of CCI, the expression (4) can be modified as below: where P is constant interference power, L is the number of interferer, hi(k) is the channel vector of the ith interferer and rest of the terms as described with reference to equa (1).A generic set-up depicting a MIMO arrangement with certain no of interferer is shown in Fig 1. Here propagation taking place through channel H while interference signal si(k) reach the receiver end through another set of channel taps denoted by .Receiver receives the CCI affected signal.
D. Kalman Filter-In 1960, R.E. Kalman published his famous paper describing a recursive solution to the discrete data linear filtering problem. The Kalman filter is a set of mathematical equations that provides an efficient computational (recursive) means to estimate the state of a process, in a way that minimizes the mean of the squared error. The filter is very powerful in several aspects: it supports estimations of past, present, and even future states, and it can do so even when the precise nature of the modelled system is unknown [8]. Kalman Filter estimation is quite common in the literature at least for single user channel. In [9] and [10] the KF is used for tracking MIMO channels based on a low order autoregressive (AR) model. However, exact modelling of fast time varying channel with a low order model is impossible since the AR functions are irrational and higher order statistics are needed.
Process to be estimated: The Kalman filter estimates the state xЄR n of a discrete-time controlled process that is governed by the linear stochastic difference equation The random variables w k and v k represent the process and measurement noise respectively. They are assumed to be independent of each other, white, and with normal probability distributions ( ) (0, ), p w N Q  The a priori state estimate at step k is defined as ˆn k x    given knowledge of the process prior to step k, and ˆn k x   to be a posteriori state estimate at step k given measurement z k . a priori and a posteriori estimate errors are The a priori estimate error covariance is then and the a posteriori estimate error covariance is [ ] An a posteriori state estimate ˆk x can be computed as a linear combination of an a priori estimate ˆk x  and a weighted difference between an actual measurement z k and a measurement prediction The difference k k z Hx   is called the measurement innovation, or the residual. The n × m matrix K is chosen to be the gain or blending factor that minimizes the a posteriori error covariance.
The specific equations for the time and measurement updates are presented in Table 1. After each time and measurement update pair, the process is repeated with the previous a posteriori estimates used to project or predict the new a priori estimates [8].

III. SYSTEM MODEL
We have considered in our setup, multiple single-user links with two CCI sources. We assume the desired user has 2 transmit antennas, the two other interfering user has 2 transmit antennas each, and there are 2 receive antennas of the desired user. Here, we have used STBC before transmission. Figure .3. Transmitter and receiver structure of co-channel interference setup.
The system model for CCI set up in wireless communication is depicted in Figure 3.The received signal at the Receiver 3 is a complex signal with CCI content. This signal is estimated with the KF and the original signal is recovered approximately in the receiver.
The state space equations for tracking the MIMO channel can be expressed as: where h is the channel tap, A is a time-varying transition matrix, C is the observation matrix and v is the measurement noise vector. On the receive antenna, the noise n has the Gaussian probability density function with with µ hi,j = 0 and σ h 2 i,j = No/2. A first-order Auto-Regressive (AR) model provides a sufficient model for time varying channels. Therefore, A can be a diagonal matrix of autoregressive model factor α, where The KF expression for MIMO channel is divided into two parts. First part is the predictor and the second part is the update is given as where, R v = βI and β is a covariance of the noise vector v. The K matrix is called the Kalman gain and the P matrix is called the estimation error covariance. Alamouti's transmit diversity space-time coding scheme relies on the availability of accurate channel state information (CSI) at the receiver. However, motion between the transmitter and the receiver results in a change in the propagation path and channel uncertainties become prevalent. To eliminate this problem, Kalman filter is used to estimate the channel.

IV. EXPERIMENTAL RESULTS
In this section, simulation results are presented. In this work, range of signal to noise ratio (SNR) considered is −10 to 10 dB. The channel experienced by each transmit antenna is independent from the channel experienced by other transmit antennas. For the transmit antenna, each transmitted symbol gets multiplied by a randomly varying complex channel matrix hi,j . As the channel under consideration is Rayleigh, the real and imaginary parts of hi,j are Gaussian distributed. of hi,j having mean µh = 0 and variance σh2 =1/2.
The channel experienced between each transmit to the receive antenna is randomly varying in time. The performance of the Kalman estimator proposed here performed satisfactorily and is better than of some similar works already reported in severely faded environments over the range of SNR −10 to 10 dB. The components of the system and channel parameters during the work are summarized in Table  II.

STBC DECODING Alamouti
The performance of the channel estimator based on Kalman filter is tested through simulations for CCI affected signal. It is seen that the estimated component nearly matches the original signal. This is observed in Figure 4. The plot shows the estimated values nearly matches the original value for up to sample no 40. But for other values there are fluctuations due to variations in the channel.  Gain is shown in the Figure 6.It is approaching the value 0 which satisfactorily show the CCI is well cancelled by the Kalman Filter. From Figure 5, we see that the estimation process fluctuates upto around 40 samples but beyond that it stabilizes. The estimate nearly matches the desired value. It means that beyond the 40 samples, the proposed approach cancels CCI better. CCI is a vital problem in the MIMO channel. In this work Kalman Filter is used to estimate the signal from the MIMO set-up filled with CCI. We specially used an application specific KF for a coded MIMO set-up which cancels CCI successfully. It shows successful recovery of the required data with around 40% of available data. The performance of the STBC coded set-up is found to be better compare to the uncoded form.