A survey of handover algorithms in DVB-H <s> RESEARCH CONDUCTED ON HANDOVER IN DVB-H <s> The 3rd generation mobile cellular communication systems will provide high-capacity bandwidth, enabling rich media and even TV services to be accessible via mobile handheld devices. For the reception of such services, seamless mobility is a must rather than an option. Alternatively, Digital Television standards, particularly data broadcasting in Terrestrial Digital Video Broadcasting (DVB-T), can be used for the delivery and reception of similar services. However, the current DVB-T standard lacks adequate methods that enable seamless mobility. In cellular delivery systems, this can be achieved by so-called soft handovers. time slicing is a recent enhancement proposed for the new - still being developed - Digital Video Broadcasting for handheld (DVB-H) standard, which together with DVB-T enables a feasible solution for soft handover to be implemented. This paper considers how time slicing can be utilized in implementing soft handover in a DVB-H receiver. An algorithm for soft handover is proposed and evaluated. <s> BIB001 </s> A survey of handover algorithms in DVB-H <s> RESEARCH CONDUCTED ON HANDOVER IN DVB-H <s> DVB-H (Digital Video Broadcasting for Handhelds) is a standard specified by the DVB Organization specifically for the broadcast of TV-like content and data to handheld devices, such as mobile phones, which have unique requirements in terms of power consumption, screen-size and mobility. Seamless handover in such a unidirectional network is especially challenging. In this paper we describe the handover issues of DVB-H networks and propose a novel seamless soft handover mechanism based on measuring CDF (Cumulative Distribution Function) of the signal to noise ratio (SNR) in the DVB-H terminal receiver front-end . Details of the algorithm is given and simulation is done to prove the benefits of such soft <s> BIB002 </s> A survey of handover algorithms in DVB-H <s> RESEARCH CONDUCTED ON HANDOVER IN DVB-H <s> DVB-H (digital video broadcasting for handheld) is one of the key technologies that enables new services, such as mobile phone TV, to be used in handhelds. DVB-H enhances mobile features found in the DVB-T standard, enabling new techniques, e.g., loss-free handover. For services such as mobile TV, loss-free handovers must be supported. Different positioning technologies, such as GPS, also play an important role in enhancing today's mobile technologies. The paper proposes a new feature for DVB-H, a new method for signalling cell coverage area, thus improving performance for loss-free handovers. The proposed method is targeted at DVB-H handhelds that have GPS receivers. The benefits of the proposed method for handover and power consumption are evaluated. In addition, its effect on the consumption of bandwidth and receiver memory is estimated. <s> BIB003 </s> A survey of handover algorithms in DVB-H <s> RESEARCH CONDUCTED ON HANDOVER IN DVB-H <s> Digital Video Broadcasting for Handhelds (DVBH) is a standard for broadcasting TV like IP data content to portable devices, such as mobile phones, personal digital assistants (PDAs), laptops, etc. Handover in unidirectional broadcasting networks is a novel issue. Since making accurate handover decisions can reduce the battery power consumed, this paper proposes and investigates different strategies that can assist the handover decision-making process in DVB-H networks. The benefits and drawbacks of the different algorithms are presented. A hybrid handover decision-making algorithm is proposed. Future research directions for handover in DVB-H are suggested. Index Terms —DVB-H, Handover, Power consumption <s> BIB004 </s> A survey of handover algorithms in DVB-H <s> RESEARCH CONDUCTED ON HANDOVER IN DVB-H <s> Mobility is a very important requirement for handheld broadcast reception terminals. It has to be ensured that a service can be continued without interruption when the user moves from one location to another. With digital video broadcasting handheld (DVB-H), such soft handovers are possible even with only one receiver front-end. In this paper it is considered how the off-times between the transmission bursts which are a feature of DVB-Hs can be used to perform those handovers. Limitations are described. A technology called "phase shifting" is proposed. This proposal was submitted to the IP datacast over DVB-H call for technologies and has been preliminary accepted in the DVB project to be added to the specification. <s> BIB005
Handover in DVB-H is a novel issue. However, much research work has already been reported in this area at the time of writing this survey. In this situation, an attempt is made to survey as far as possible the work that has been reported and forecast the work that will be done. An instantaneous Received Signal Strength Indication (RSSI) value based handover scheme was proposed in BIB001 . This handover scheme is the first for DVB-H published in the literature. This scheme uses the off burst time to measure the RSSI value. After comparing the current RSSI value with that of adjacent cells, it hands over to the cell with the strongest RSSI value. The handover stages for this handover algorithm are shown in Figs. 12 and 13. Since the RSSI value can vary due to multipath, interference or other environmental effects it may not give a true indication of the communication performance or the range and mistakenly measuring the RSSI value would result in the Ping Pong effect in handover measurement consuming power unnecessarily. The RSSI value could be measured many off burst times with the RSSI value being measured at least once every off burst time in the worst case. Constant measuring of the adjacent cells signal level without any handover prediction leads to more battery power consumption. In order to overcome these shortcomings, a better handover prediction algorithm had to be developed. Hamara presented an enhanced version of the algorithm of BIB001 in his thesis  where, in addition to using the RSSI value as a handover criterion, currently consumed services and bit error rate were taken into account. This thesis is the first thesis about DVB-H handover in the literature. It gives an extensive analysis of the handover aspects within DVB-H in the light of the standard solutions at the time. In BIB002 another handover scheme based on post-processing of the measured SNR value was proposed to avoid the Ping Pong effect and to get rid of the received "fake signals." In the SNR-based handover scheme, the SNR is calculated from the RSSI and the noise characteristics and provides a more accurate estimate of the received effective signal than the RSSI. BIB001 . Step 4 Step 3 Step 2 Step 1 Step 5 Step 6 Step 7 Start probability of receiving that outcome or a lower one. Because the CDF gives a probability value, its value depends not only on the current SNR value, but also on the SNR history of the signal. This not only eliminates the frequent handover phenomenon seen in instantaneous RSSI value-based handover, but also avoids the "fake signals" caused by frequency confusion. Although simulation has shown the feasibility of this simple algorithm, further studies and field trials need to be done to investigate the limitations of this algorithm. Vare, Hamara, and Kallio BIB003 have proposed a new method for signaling cell coverage areas by means of bitmap data to improve the handover performance in DVB-H. A new table called the Cell Description Table (CDT) is proposed for the PSI/SI. By using a CDT, up to 256 different signal levels within the cell coverage area can be signaled to the receiver to inform it of the cell coverage. The terminal can make better handover decisions from the information about the cell coverage area to reduce the Ping Pong effect and "fake signals." However, in this proposed handover scheme more bandwidth and receiver memory consumption is needed to support the CDT information process. In addition, the DVB-H handheld receiver must have GPS support which will be an additional cost to the customer. This kind of cost cannot be neglected, especially in the early DVB-H roll out stage when potential customers are still not fully convinced of the benefits of DVB-H services. Transferring the cost from the terminal side to the network side is an alternative solution if the network can provide the same location information to the terminal as a GPS receiver does. Yang et al. BIB004 investigated different handover decisionmaking algorithms and proposed a novel hybrid handover decision-making algorithm. The key idea of BIB004 is to reduce the frequency of handover measurement in the handover decision-making stage by designing a soft handover algorithm with prediction of the handover moment. The proposed handover decision-making algorithms are Context-Aware Handover Decision-making, Location-Aided Handover Decision-making, UMTS Aided Handover Decision-making, Repeater-Aided Handover Decision-making, and Hidden Markov Model Based Decision-making. A comparison of the different handover decision-making algorithms is presented in Table 1 according to BIB004 . As a conclusion to BIB004 , a hybrid handover decision-making algorithm is proposed that can utilize the advantages of the different handover decision-making algorithms while eliminating the limitations of them by using a central management module to control the choice of one of the different handover modules in different environment scenarios. The feasibility and the limitations of the proposed handover decision-making algorithm need to be validated through field trials. A more detailed description of different handover algorithms, especially of the different handover decision-making algorithms in dedicated DVB-H networks and in converged DVB-H/UMTS networks, is presented in  . The investigation and research of the handover in converged DVB-H and UMTS networks is thought to be one of the first in the literature. Schwoerer   and Vesma  target power consumption reduction by utilizing novel synchronization techniques in the handover execution stage of the handover process. The handover execution stage is equal to the signal synchronization, and the on time in the time slicing mode consists of both the synchronization time and the burst data duration time, as shown in Fig. 14 ; the main idea of   is to try to minimize the synchronization time to further reduce the power consumption. The main exploitable synchronization time in the synchronization stage is the TPS synchronization, as shown in Fig. 15  . Schwoerer and Vesma  proposed a new synchronization technique called correlation-based "Fast Scattered Pilot Synchronization" for DVB-H receivers to substitute the connFigure 13. Decision-making and execution stages of the handover algorithm according to BIB001 . Step 1 Step 2 Step 6 Step 5 Step 3 Step 4 ventional TPS-based OFDM frame synchronization for finding the position of Scattered Pilots within an OFDM symbol in the handover execution stage. It exploits the temporally repetitive structure of the scattered pilots and Schwoerer and Vesma  showed using mathematical analysis that the synchronization time (until channel estimation) could be cut by 84 percent by using the new technique. Reducing the synchronization time means reducing the power consumption. Therefore, "Fast Scattered Pilot Synchronization" can reduce the power consumption in the DVB-H handover execution stage. Schwoerer  proposed another purely power-based "Fast Scattered Pilot Synchronization" method. It uses the fact that scattered pilots are amplitude-boosted by 4/3 to find the current Scattered Pilot Raster Position (SRPR)  . It is shown in  that 89 percent of the synchronization time can be saved using power-based "Fast Scattered Pilot Synchronization." In BIB005 May focused on the handover execution stage of the handover process in DVB-H. Because the IP network delay and jitter may be different for different cells May proposed a technology called "phase shifting" to synchronize the signals of adjacent cells in IP Datacast over DVB-H networks in order to ensure loss-free handovers. When the terminal moves from one cell to another, synchronization techniques must be used to ensure that there is no packet loss caused by a time sliced burst overlap when the next time sliced burst arrives. There are three different possibilities for the types of synchronization. The first is no synchronization that of course will cause considerable packet loss. The second is in-phase synchronization where all the transport streams in different cells must be transmitted in perfect synchronization, that is, at the same universal time. This cannot be ensured without a buffer system in the network side. The third one is "phase shifting" synchronization where there is a time shift between adjacent cells to ensure that there is enough time between the neighboring time slices to avoid the possible packet loss caused by time slice overlap. The phase shifting principal for handover between any two cells as a four-color problem  is illustrated in Fig. 16 according to BIB005 . Analysis and simulation showed that the phase shifting synchronization techniques can achieve much better performance with respect to the packet loss probability compared with the no synchronization and "in phase" synchronization techniques. The DVB Project technical reports [45] and [16] proposed a simple handover algorithm for handover in DVB-H based on the handover algorithm in DVB-T. The basic idea is for the DVB-H terminal to use the terrestrial_delivery_system_descriptor, the frequency_list descriptor, the original_network_id and the transport_stream_id together as a pair along with the service_list_descriptor to decide which frequency and transport stream the receiver should switch to in the handover process. Several methods to reduce the risk of tuning failures or "fake signals" are also presented. The first one proposed in [45] is called "local SI insertion" which makes each cell a separate network by individual Service Information (SI) insertion. In this case, there will be only one frequency per network. The second method utilizes the cell identifier so the terminal can know which cell it has entered. In this case, the terminal can determine and check the cell id of a signal from its TPS bits to see if it is in its cell id list of interest after checking the frequency thus reducing the tuning failure. The third method uses location data from GPS receivers to aid the handover so the terminal can determine the destination cell reducing tuning failure. The last method in [45] uses two front-ends including a second demultiplexer. In this case, the tuning of different frequencies can be done in parallel and the target cell frequency can be validated in advance so that the risk of tuning failure can be completely eliminated.