1. Field of the Invention
The present invention relates, generally, to a rake receiver for telecommunication systems with wireless telecommunication between mobile and/or stationary transceivers, and, more particularly, to such a rake receiver wherein a pipeline architecture having a number of pipeline stages is employed such that individual signal processing steps are processed as on a pipeline.
2. Description of the Prior Art
Telecommunication systems with wireless telecommunication between mobile and/or stationary transceivers are special communication systems with an information transmission link between a message source and a message sink in which, for example, base stations and mobile parts are used as transceivers for message processing and transmission and in which:    1) the message processing and message transmission can take place in a preferred direction of transmission (simplex mode) or in both directions of transmission (duplex mode);    2) the message processing is preferably digital; and    3) the message transmission via the long-distance link takes place wirelessly on the basis of various message transmission methods FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and/or CDMA (Code Division Multiple Access)—e.g., according to radio standards such as            DECT [Digital Enhanced (previously European) Cordless Telecommunication; compare Nachrichtentechnik Elektronik 42 (1992) January/February No. 1, Berlin, DE, U. Pilger “Struktur des DECT-Standards” [Structure of the DECT standard], pages 23 to 29 in conjunction with ETSI publication ETS 300175-1 . . . 9, October 1992 and DECT publication of the DECT Forum, February 1997, pages 1 to 16], GSM [Group Spéciale Mobile or Global System for Mobile Communication; compare Informatik Spektrum 14 (1991) June, No. 3, Berlin, DE; A. Mann. “Der GSM-Standard—Grundlage für digitale europäische Mobilfunknetze” [The GSM standard—The basis for digital European mobile radio networks], pages 137 to 152 in conjunction with the publication telekom praxis 4/1993, P. Smolka “GSM-Funkschnittstelle—Elemente und Funktionen” [GSM radio interface—elements and functions], pages 17 to 24],        UMTS [Universal Mobile Telecommunication System; compare (1): Nachrichtentechnik Elektronik, Berlin 45, 1995 vol. 1, pages 10 to 14 and vol. 2, pages 24 to 27; P. Jung, B. Steiner: “Konzept eines CDMA-Mobilfunksystems mit gemeinsamer Detektion für die dritte Mobilfunkgeneration” [Concept of a CDMA mobile radio system with joint detection for the third mobile radio generation]; (2): Nachrichten-technik Elektronik, Berlin 41, 1991, vol. 6, pages 223 to 227 and page 234; P. W. Baier, P. Jung, A. Klein: “CDMA—ein günstiges Vielfach-zugriffsverfahren für frequenzselektive und zeitvariante Mobilfunkkanäle” [CDMA—an advantageous multiple access method for frequency-selective and time-variant mobile radio channels], (3): IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. E79-A, No. 12, December 1996, pages 1 930 to 1 937; P. W. Baier, P. Jung: “CDMA Myths and Realities Revisited”; (4): IEEE Personal Communications, February 1995, pages 38 to 47; A. Urie, M. Streeton, C. Mourot: “An Advanced TDMA Mobile Access System for UMTS”; (5): telekom praxis, 5/1995, pages 9 to 14; P. W. Baier: “Spread-Spectrum-Technik und CDMA—eine ursprünglich militärische Technik erobert den zivilen Bereich” [Spread-spectrum technology and CDMA—a technology originally from the military domain conquers the civil domain], (6): IEEE Personal Communications, February 1995, pages 48 to 53; P. G. Andermo, L. M. Ewerubring: “A CDMA-Based Radio Access Design for UMTS”; (7): ITG Fachberichte 124 (1993), Berlin, Offenbach: VDE Verlag ISBN 3-8007-1965-7, pages 67 to 75; Dr. T Zimmermann, Siemens A G: “Anwendung von CDMA in der Mobilkommunikation” [Application of CDMA in mobile communication], (8): telcom report 16, (1993), vol. 1, pages 38 to 41, Dr. T Ketseoglou, Siemens A G and Dr. T Zimmermann, Siemens A G: “Effizienter Teilnehmerzugriff für die 3. Generation der Mobilkommunikation—Vielfachzugriffsverfahren CDMA macht Luftschnittstelle flexibler” [Efficient subscriber access for the 3rd-generation mobile communication—CDMA multiple access method makes the interface more flexible]; (9): Funkschau 6/98: R. Sietmann “Ringen um die UMTS-Schnittstelle” [Tug-of-war for the UMTS interface] pages 76 to 81] WACS or PACS, IS-54, IS-95, PHS, PDC etc. [compare IEEE Communications Magazine, January 1995, pages 50 to 57; D. D. Falconer et al.: “Time Division Multiple Access Methods for Wireless Personal Communications”].        
“Message” is a higher-level term which stands both for the meaning (information) and for the physical representation (signal). In spite of identical meaning of a message, that is to say identical information, different signal forms can occur. Thus, for example, a message relating to an object can be transmitted    (1) in the form of an image,    (2) as a spoken word, or    (3) as a written word,    (4) as an encrypted word or image.
The type of transmission according to (1) . . . (3) is normally characterized by continuous (analog) signals whereas it is usually discontinuous signals (e.g. pulses, digital signals) which are produced with the type of transmission according to (4).
In the UMTS scenario (3rd-generation mobile radio or, respectively, IMT 2000), there are two part-scenarios, for example according to the printed document Funkschau 6/98: R. Sietmann “Ringen um die UMTS-Schnittstelle” [Tug-of-war for the UMTS interface], pages 76 to 81. In a first part-scenario, the licensed coordinated mobile radio will be based on a WCDMA (Wideband Code Division Multiple Access) technology and operated in FDD (Frequency Division Duplex) mode as in GSM, whereas, in a second part-scenario, the unlicensed uncoordinated mobile radio will be based on a TD-CDMA (Time Division Code Division Multiple Access) technology and operated in TDD (Time Division Duplex) mode as in DECT.
For the WCDMA/FDD operation of the universal mobile telecommunication system, the air interface of the telecommunication system in each case contains a number of physical channels in the uplink and downlink direction of telecommunication in accordance with the printed document ETSI STC SMG2 UMTS-L1, Tdoc SMG2 UMTS-L1 163/98: “UTRA Physical Layer Description FDD Parts” vers. 0.3, May 5, 1998, of which channels a first physical channel, the so-called Dedicated Physical Control Channel DPCCH, and a second physical channel, the so-called Dedicated Physical Data Channel DPDCH, are shown with respect to their frame structures in FIGS. 1 and 2.
In the downlink (radio link from the base station to the mobile station) of the WCDMA/FDD system by ETSI and ARIB, respectively, the Dedicated Physical Control Channel (DPCCH) and the Dedicated Physical Data CHannel (DPDCH) are time-division multiplexed whereas in the uplink, an I/Q multiplex is done in which the DPDCH is transmitted in the I channel and the DPCCH is transmitted in the Q channel.
The DPCCH contains Npilot pilot bits for channel estimation, NTPC bits for fast power control and NTFI format bits which indicate the bit rate, the type of service, the type of error protecting coding, etc. (TFI=Traffic Format Indicator).
FIG. 3 shows, on the basis of a GSM radio scenario which includes, for example, two radio cells and Base Transceiver Stations arranged therein, a first base transceiver station BTS1 (transceiver) omnidirectionally illuminating a first radio cell FZ1 and a second base transceiver station BTS2 (transceiver) omnidirectionally illuminating a second radio cell FZ2, an FDMA/TDMA/CDMA radio scenario in which the base transceiver stations BTS1, BTS2 are connected or can be connected to a number of mobile stations MS1 . . . MS5 (transceiver) located in the radio cells FZ1, FZ2 by wireless unidirectional or bi-directional-uplink UL and/or downlink DL—telecommunication on corresponding transmission channels TRC via an air interface designed for the FDMA/TDMA/CDMA radio scenario. The base transceiver stations BTS1, BTS2 are connected in at familiar manner (compare GSM telecommunication system) to a base station controller BSC which handles the frequency administration and switching functions in controlling the base transceiver stations. The base station controller BSC, in turn, is connected via a Mobile Switching Center MSC to the higher-level telecommunication network; e.g., the PSTN (Public Switched Telecommunication Network). The mobile switching center MSC is the administrative center for the telecommunication system shown. It handles the complete call administration and, with attached registers (not shown), the authentication of the telecommunication subscribers and the location monitoring in the network.
FIG. 4 shows the basic configuration of the base transceiver station BTS1, BTS2 constructed as transceiver and FIG. 5 shows the basic configuration of the mobile station MS1 . . . MS5, also constructed as transceiver. The base transceiver station BTS1, BTS2 handles the transmitting and receiving of radio messages from and to the mobile station MS1 . . . MS5 and the mobile station MTS1 . . . MTS5 handles the transmitting and receiving of radio messages from and to the base transceiver station BTS1, BTS2. For this purpose, the base station has a transmitting antenna SAN and a receiving antenna EAN and the mobile station MS1 . . . MS5 has a common antenna ANT for transmitting and receiving which is controllable by an antenna switch AU. In the uplink (receiving path), the base transceiver station BTS1, BTS2 receives via the receiving antenna EAN, for example, at least one radio message FN with an FDMA/TDMA/CDMA component from at least one of the mobile stations MS1 . . . MS5 and the mobile station MS1 . . . MS5 receives in the downlink (receiving path) via the common antenna ANT, for example, at least one radio message FN with an FDMA/TDMA/CDMA component from at least one base transceiver station BTS1, BTS2. The radio message FN consists of a broadband spread-spectrum carrier signal modulated with an information item composed of data symbols.
In a radio receiver FEE, the received carrier signal is filtered and mixed down to an intermediate frequency which, in turn, is thereafter sampled and quantized. After analog/digital conversion, the signal, which has been distorted by multipath propagation on the radio path, is supplied to an equalizer EQL which largely equalizes (synchronizes) the distortions.
After that, a channel estimator KS attempts to estimate the transmission characteristics of the transmission channel TRC on which the radio message FN has been transmitted. The transmission characteristics of the channel are specified by the channel impulse response in the time domain. To be able to estimate the channel impulse response, a special supplementary information item in the form of a so-called midamble, which is designed as training information sequence, is assigned or allocated to the radio message FN at the transmitting end (by the mobile station MS1 . . . MS5 or, respectively, the base transceiver station BTS1, BTS2, in the present case).
The individual mobile-station-specific signal components, which are contained in the common signal, are equalized and separated in a known manner in a subsequent data detector DD which is common to all received signals. After the equalization and separation, the data symbols hitherto present are converted into binary data in a symbol-to-data converter SDW. After that, the original bit stream is obtained from the intermediate frequency in a demodulator DMOD before the individual time slots are allocated to the correct logical channels and, thus, also to the different mobile stations in a demultiplexer DMUX.
The bit sequence obtained is decoded channel by channel in a channel codec KC. Depending on the channel, the bit information is allocated to the control and signaling timeslot or to a voice timeslot and, in the case of the base transceiver station (FIG. 4), the control and signaling data and the voice data are jointly transferred to an interface SS responsible for the signaling and voice coding/decoding (voice codec) for transmission to the base station controller BSC. In the case of the mobile station (FIG. 5), the control and signaling data are transferred to a control and signaling unit STSE responsible for the complete signaling and control of the mobile station and the voice data are transferred to a voice codec SPC designed for voice input and output.
In the voice codec of the interface SS in the base transceiver station BTS1, BTS2, the voice data is in a predetermined data stream (e.g., 64-kbit/s stream in the direction of the network and 13 kbit/s stream in the direction from the network).
The complete control of the base transceiver station BTS1, BTS2 is performed in a control unit STE.
In the downlink (transmitting path), the base transceiver station BTS1, BTS2 sends via the transmitting antenna SAN, for example, at least one radio message FN with an FDMA/TDMA/CDMA component to at least one of the mobile stations MS1 . . . MS5 and the mobile station MS1 . . . MS5 sends in the uplink (transmitting path) via the common antenna ANT, for example, at least one radio message FN with an FDMA/TDMA/CDMA component to at least one base transceiver station BTS1, BTS2.
The transmitting path begins at the base transceiver station BTS1, BTS2 in FIG. 4, by control and signaling data and voice data received by the base station controller BSC via the interface SS being assigned to a control and signaling timeslot or a voice timeslot in the channel codec KC and these timeslots being coded in a bit sequence channel by channel.
The transmitting path begins in the case of the mobile station MS1 . . . MS5 in FIG. 5 by voice data received from the voice codec SPC and control and signaling data received from the control and signaling unit STSE being assigned to a control and signaling timeslot or a voice timeslot in the channel codec KC and these timeslots being coded in a bit sequence channel by channel.
The bit sequence obtained in the base station BTS1, BTS2 and in the mobile station MS1 . . . MS5 is, in each case, converted into data symbols in a data-to-symbol converter DSW. Following this, the data symbols are, in each case, spread with a subscriber-associated code in a spreader SPE. In the burst generator BG consisting of a burst assembler BZS and a multiplexer MUX, a training information sequence in the form of a midamble is then added to the spread data symbols in the burst assembler BZS for channel estimation and the burst information obtained in this manner is set to the correct timeslot in the multiplexer MUX. The burst obtained is then radio-frequency modulated, in each case, in a modulator MOD and digital/analog converted before the signal obtained in this manner is radiated at the transmitting antenna SAN or, respectively, the common antenna ANT via a radio transmitter FSE as radio message FN.
In CDMA-based systems, the problem of multiple reception, the so-called delay spread, in the presence of echoes can be solved in spite of the great bandwidth and the very small chip or bit times of these systems by combining the received signals with one another in order to increase the reliability of detection. Naturally, the channel characteristics must be known for this. To determine these, a pilot sequence common to all subscribers is used (compare FIGS. 1 and 2) which is additionally radiated independently and with increased transmitting power without modulation by a message sequence. Its reception provides the receiver with the information on how many paths are involved in the instantaneous situation of reception and what delay times are produced.
In a RAKE receiver, the signals coming in via the individual paths are acquired in separate receivers, the “fingers” of the RAKE receiver, detected and added together in an addition section weighted among each other after compensation for the delay times and the phase shifts of the echoes.
A RAKE receiver is used, in particular, for recovering digital data from a radio reception signal having a CDMA component. The signals superimposed via multipath propagation and distorted by the channel are recovered and the symbol energies of the individual propagation paths are accumulated.
The theory for the RAKE receiver has been sufficiently well investigated and is known (compare J. G. Proakis: “Digital Communications”; McGraw-Hill, Inc.; 3rd edition, 1995; pp. 728 to 739 and K. D. Kammeyer: “Nachrichtenübertragung” [Information transmission]; B:G. Teubner Stuttgart, 1996; pp. 658 to 669).
An object of the present invention is to specify a rake receiver for telecommunication systems with wireless telecommunication between mobile and/or stationary transceivers, especially in third-generation mobile radio systems, which exhibits a smaller number of function blocks and/or logic gates compared with known rake receivers.
Accordingly, the present invention has a pipeline architecture, including a number of pipeline stages (pipeline structure), which is implemented such that the individual signal processing steps or computing steps are processed as in a pipeline. As a result, the hardware circuits used can be used in time-division multiplex.
In an embodiment, it is advantageous to use three pipeline stages. It is also advantageous to buffer the processing in the pipeline stages via two registers if no direct pipelining is possible in the three pipeline stages because of different processing speeds in the pipeline stages.
In a first pipeline stage, the data (e.g., chips or subchips in the case of oversampling) are read out of a memory (e.g., a dual-port RAM (DP-RAM)). To be able to superimpose the symbols of the individual signal paths in the correct phase (code combining), the corresponding path delays must be taken into consideration. The addresses are also calculated in the first stage. The delay time is added to the current address in the form of an offset. There are, for example, “L” offsets, “L” corresponding to the number of fingers in the RAKE receiver and a different offset being needed in each clock period. Thus, the memory is accessed in every clock period.
Furthermore, the code generated by at least one code generator, the spreading code and/or the scrambling code required for descrambling, is multiplied by the current value from the dual-port RAM in the first pipeline stage. This operation is relatively simple since it only consists of sign operations and of two additional additions in the case of complex scrambling codes.
In addition, the soft handover is handled in the first pipeline stage. In the case of a soft handover, the RAKE receiver receives signals which have been sent with different scrambling and spreading codes from, for example, base transceiver stations. The maximum possible number of RAKE fingers must be shared out among the base transceiver stations in accordance with the quality of reception. For this reason, the code generators are switched in dependence on the RAKE fingers. The multiplexer performing the switching operates at a maximum of L*W MHz. To increase the number of base transceiver stations, further code generators can be added.
In the second pipeline stage, each value is multiplied by a weight. These weights are different for each finger and change with every clock period. In principle, they are repeated after “L” steps. In the case of an interpolation, the delta values are accumulated to form the weights.
In the last, third pipeline stage, the chip energies of the individual RAKE fingers are accumulated to form the symbol energy Usymb.
                    u        symb            =                        ∑                      i            =            1                    SF                ⁢                                  ⁢                              ∑                          j              =              1                        L                    ⁢                                          ⁢                      u            ij                                ;                  where        ⁢                                  ⁢        SF            =              spreading        ⁢                                  ⁢        factor              ,      L    =          number      ⁢                          ⁢      of      ⁢                          ⁢      RAKE      ⁢                          ⁢              fingers        .            
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawings.