Abstract:
The present invention encompasses an electronic device operated in a communication system (for example 1XEV-DO, 1XEV-DV, CDMA, etc). The electronic device receiving a signal from a base station, the signal containing signaling information and data packets. The electronic device processing portion of the signal during the current frame and simultaneously storing the received signal prior to de-spreading, for further processing during the following frame. The electronic device further processing previously stored signal, during current frame.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a communication technique used in a wireless communication system and, more particularly, to a receiver for processing a received signal from a base station.  
         BACKGROUND OF THE INVENTION  
         [0002]    A communication system is formed, at a minimum, of a base station and a mobile station, which are interconnected by way of a communication channel. Information to be communicated by the base station (also referred to as cell site) to the mobile station is transmitted via the communication channel to the mobile station. A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of information between base stations and mobile stations.  
           [0003]    A wireless communication system, is an example of a communication system, which has been made possible due to advancements in communication technologies. Various standards have been promulgated relating to various types of wireless communication systems, and various types of wireless, as well as other, communication systems have been constructed, corresponding to such standards. The IS-95 and IS-2000 interim standards, promulgated by the EIA/TIA, are exemplary of standards which pertain to a wireless communication system, utilizing code division multiple access (CDMA) communication techniques.  
           [0004]    Enhanced 3 rd  Generation CDMA systems are currently being developed to address high speed Internet packet data services. Examples of such systems, which are the result of an evolution of IS-95 and IS2000, are 1XEV-DO (TIA/EIA/IS-856) and 1XEV-DV standards. These systems utilize both CDMA and some type of time division multiplexing communication techniques.  
           [0005]    In an effort to port the Internet to the wireless communication system, 1 XEV-DO and 1 XEV-DV systems use a fat data pipe concept, which is shared among a number of users (mobile stations). The fat pipe, called the shared supplemental channel, is de-multiplexed into several code channels according to the usual CDMA access techniques. In the current proposal for 1XEV-DV, for example, the pipe is actually transmitted on 14 or 15 Walsh codes of length 16.  
           [0006]    In high data rate systems, it is assumed that low mobility prevails and the use of soft handoff is not needed. Also, use of soft handoff would reduce the data rate capacity of the system. Therefore, a fast cell site selection is performed in the network, aided by measurements made at the mobile station. However, the mobile station can only assist the BS by sending information on the reverse link. Because of impairments on the reverse link, the BS may actually select a less then preferred cell site. instead of the preferred target cell site  
           [0007]    In the high data rate, the shared supplemental channel is shared among a number of mobile stations in accordance with CDMA and TDMA communication techniques. The base station has an admission control algorithm such that the base station decides 1) when to transmit data packets to a particular mobile station; 2) the modulation type and coding rate; 3) the Walsh codes (among the 14 or 15 available) that will be assigned; and 4) the cell site that will transmit the data packets.  
           [0008]    The BS simultaneously transmits the data packet, intended for the mobile station, on the supplemental channel and a signaling frame on the dedicated channel. This signaling frame provides the mobile station information such as 1) whether a data packet was sent to that MS; 2) the modulation type and coding rate used; 3) the Walsh codes; and 4) which cell site is transmitting on shared supplemental channel. Upon reception of a signaling frame, the mobile station decodes the dedicated channel and determines if there was a data packet for it on the shared supplemental channel. Thus, the mobile station is expected to buffer the received shared supplemental channel information in order to be able, after the fact, demodulate and decode the share supplemental channel. Generally, the dedicated channel and all the supplemental channels are de-spread to retrieve necessary information and all the expanded information is stored is a buffer. Generally, the buffer size required depends on the number of fingers needed, the number of Walsh channels, the sampling rate, etc. Since the mobile station must de-spread all the Walsh channels to determine if a data packet is transmitted for that MS, a large buffer size is needed, even if only one Walsh channel may apply.  
           [0009]    Therefore, it would be useful if method and apparatus was provided to manage the buffering and processing of signals that would require less storage space and processing time.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention, accordingly, advantageously, provides apparatus, and an associated method by which received communication signals are first stored in RAM and then processed.  
           [0011]    The present invention encompasses a receiver having a buffer storing a received signal and replaying the received signal to process only a necessary portion of the signal. The buffer may comprise a plurality of buffers, wherein a received signal for a current frame is stored in a first buffer and a second buffer is used to process the signal received in a previous frame. According to an aspect of the invention, the received signal is stored in buffer prior to de-spreading the signal, thereby, advantageously requiring less storage space for the buffer. Once the signal is stored for a frame, during the next frame the signal may be evaluated to determine is any data for the mobile station has been transmitted on a shared supplemental channel. The signal is further processed only if data packets for that mobile station have been transmitted on the shared supplemental channel. Otherwise, advantageously, no further processing is performed on the signal to find data.  
           [0012]    A more complete appreciation of the invention and to the scope thereof can be obtained from the accompanying drawings, the detailed description of the presently preferred embodiments of the invention, and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 illustrates a block diagram of an exemplary receiver used in a wireless communication system;  
         [0014]    [0014]FIG. 2 illustates a flowchart for a method of operating a reciever;  
         [0015]    [0015]FIG. 3 illustrates a block diagram of a second embodiment of a receiver used in a wireless communication system; and  
         [0016]    [0016]FIG. 4 illustates a flowchart for method of operating a receiver according to a second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 illustrates an exemplary wireless communication system  100 . The communication system  100  provides for radio communication between two communication stations, such as a base station  102  and a mobile station  104 , by way of radio links formed therebetween. The mobile station  104  is configured to receive and transmit signals to communicate with plurality of base stations, including base station  102 . In the exemplary embodiment shown in the figure, the communication system  100  operates according to the specification proposed for 1XEV-DO (approved version IS-856/TSG-C C.S0024 ver 2.0, published 10/2000) and 1XEV-DV (current proposal # C05-20010611-007 MNTIPA — 1 XEV-DV L1 Framework) communication system, which utilizes CDMA communication techniques. It should be understood that operation of the embodiment of the present invention is similarly also possible in other types of radio, and other, communication systems. Therefore, while the following description shall describe operation of an embodiment of the present invention with respect to the 1XEV-DO or 1XEV-DV systems, operation of an embodiment of the present invention can analogously be described with respect to any of various other types of communication systems.  
         [0018]    The base station  102 , is coupled to a base station controller (BSC)  140 . And, the base station  102  is, in turn, coupled to a mobile switching center (MSC)  142 . The MSC is coupled to a network backbone, here a PSTN (public switched telephonic network)  144 , and correspondent node (CN)  146  is coupled to the PSTN  144 . A communication path is formable between the correspondent node  146  and the mobile station  104  by way of the PSTN  144 , the MSC  142 , the BSC  140  and base station  102 , and a radio link formed between the base station and the mobile station. Thereby, the communications, of both voice data and non-voice data, are effectual between the CN  146  and the mobile station  104 . In the exemplary implementation as shown in the figures, the base station defines a cell, and numerous cell sites are positioned at spaced-apart location throughout a geographical area to define a plurality of cells within any of which the mobile station  104  is capable of radio communication with an associated base station to communication therewith.  
         [0019]    In the operation of the communication systems  100  according to 1XEV-DO and 1XEV-DV systems, the base station  102  transmits spread spectrum signals to mobile station  104  on what is generally known as the forward link. In general, the forward link transmission comprises a plurality of frames defined by the proposed system specification. In the exemplary communication system, the signals are received substantially during the reception a frame on plurality of channels (forward link channels), generally comprising signals for a pilot channel, control channels, supplemental channels and dedicated channels. The supplemental channels comprise interleaved and spread data signals. The dedicated channel comprise signaling information about the data transmitted on the supplemental channels.  
         [0020]    The base station  102  broadcasts on the forward link channels, for example, on a pilot channel, a paging channel, a control channel, a dedicated channel and a plurality of supplemental channels. Generally, all the supplemental channels are spread using a Walsh Code in a process known as Walsh covering. Additionally, all the channels are modulated using a modulation-coding scheme (MCS) having a modulation type and coding rate. The modulation schemes are defined by the type of system, such as 1-XEVDO or 1XEV-DV, wherein each mobile station, in communication with one or more base stations, provides information, such as Carrier to Interference ratios (C/I) or Signal to Noise Ratio (SNR), to assist base stations in determining modulation type and coding rate.  
         [0021]    In the exemplary communication systems, the supplemental channels are shared among a plurality of mobile stations (MS), including mobile station  104 . The base station  102  operates according to an admission control algorithm which determines, when to transmit data packets to a particular mobile station, what modulation type and coding rate is used, which Walsh codes will be assigned to the mobile station, and which base station of the system will transmit. In the exemplary communication system according to 1XEV-DV, the supplemental channels typically comprise up to 16 channels (Walsh channels), wherein any one of the channels may contain a packet of data for a particular mobile station. Each of the Walsh channels is spread using a different Walsh covering.  
         [0022]    In the exemplary communication systems, the base station simultaneously transmits a packet of data and signaling information. The signaling information indicates to the mobile station  104  that the packet of data is sent to the mobile station  104 . The signaling information to determine the processing of supplemental channels, wherein the signaling information comprises the modulation type and the code rate, the Walsh codes that are utilized, and which base station is transmitting on the supplemental channels.  
         [0023]    The mobile station  104 , operable in 1XEV-DO and 1XEV-DV systems, comprises an antenna  106 , a front end filter  108 , an analog to digital (A/D) converter  110 , a Random Access Memory (RAM)  112 , a Rake receiver  118 , an Interpolator  128 , a Master controller  130  and a decoder  132 . The antenna  106  receives radio frequency (RF) signals (forward link) from the base station  102  and from other base stations in the vicinity. The received RF signals are converted to electrical signals by the antenna  106  and provided to the front end  108 . The front end  108  filters the signals and provides conversion to baseband signals. The baseband signals are provided to the AD converter  110 , which converts the baseband signals to digital signals for further processing.  
         [0024]    In accordance with the an embodiment of the invention, the received signal (also referred to as current frame signal) is stored in Random Access Memory (RAM)  112  prior to any de-spreading of the signal. The RAM  212  comprises first and second buffers  114  and  116 . In an exemplary embodiment, the first buffer  114  may be used to store a current frame signal and the second buffer  116  may be used to store a previous frame signal. The master controller  130 , coupled to the RAM  114 , comprises logic to toggle the use between first buffer  114  and second buffer  116 . Because the signal is stored before de-spreading the signal, the memory size requirement is significantly less then if the signal was stored after de-spreading the signal. Since, the converted signal is stored in the buffer  114  or buffer  116  prior to de-spreading, advantageously system time tick  2  samples per chip may be used. Therefore, for example, the buffer size of first and second buffers,  114  and  116 , may be 98304 bits or 12.3 kbytes, generally calculated using 6144 (chips)×2 samples×4 bits×2 (I and Q) equaling to approximately 98304 bits. It should be noted that size of the RAM  112 , the first and second buffers,  114  and  116 , might vary based on the manufacturers desired sampling rate and other factors.  
         [0025]    The Rake receiver  118  is a conventional receiver comprising a sample selector  120 , a correlator  122 , a Walsh de-spreader  124  and a symbol combiner  126 . The Rake receiver  118  processes the signal received on the dedicated channel to determine signaling information and sends the signaling information to a master controller  130 . Using well-know techniques, the Rake receiver  118 , extracts all the information necessary for master controller  130  to efficiently evaluate the supplemental channel data stored in RAM  112 . The signaling information generally comprises an indication that a packet data for a particular mobile station is on the supplemental channel. The signaling information further comprises the Walsh codes, the number of supplemental channel, modulation type and coding rate used by the BS. Additionally, the signaling information may comprise a system time counter, pseudo-random noise states and Long code states.  
         [0026]    The master controller  130  comprises logic to control the operations of all the components of the receiver. The master controller  130  includes a clock  131 . The clock controls timing of the mobile station  104 . The master controller  130  is coupled to the other elements of the mobile station  104  and such interconnections are not shown so as to not unduly complicate the drawing figure.  
         [0027]    In an operation of an embodiment of the present invention, for every frame, the conventional rake receiver  118  of the receiver  104 , processes the dedicated channel of the received signal. The rake receiver  118  extracts the signaling information for the current frame and sends the signaling information to the master controller  130  via the decoder  132 . Simultaneously, the signal, which contains all channels, including the supplemental channels, is stored in RAM  112 . The master controller  130  determines which one of the buffers, first buffer  114  or second buffer  116 , to use. Generally, one buffer is used to store current frame signal and the other buffer is used to store previous frame data. Simultaneously, the master controller  130  having soft information from the previous frame, replays the previous frame data stored in RAM  112  to process the data using the soft information. The master controller  130  only replays the stored data, if the soft information indicates that a packet data for mobile station  104  is in the signal received on the supplemental channel. The master controller  130  determines which buffer to use for storing the current frame signal.  
         [0028]    The master controller  130  comprises logic to decode the signaling information comprising the modulation type, coding rate, the Walsh codes assigned to the mobile station and the base station that transmitted the data. Using the Walsh code assignment extracted from the soft information, the master controller  130  processes the control channel and thereafter despreads the supplement channels to extract the data packets as defined in the 1XEV-DO and 1XEV-DV specification. The master controller  130  also comprises logic to control the operation of the interpolator  128  for generating the best sampling instant for the correlator  122 . The master controller  130  uses the signaling information from Rake receiver to program the interpolator  128 .  
         [0029]    An interpolator  128  may be single hardware unit, used in a time divisional method (i.e. time shared). The interpolator  128  according to invention, controlled by a master controller  130 , for generating best sampling instances.  
         [0030]    [0030]FIG. 2 illustrates flowcharts of tasks, generally shown as  200 ,  250  and  270 , which are executed simultaneously during each frame. In the preferred embodiment of the invention the master controller  130  simultaneously executes tasks,  200  and  250 , and the Rake receiver  118  executes task  270 . Task  200  handles the reception of the communication signal during the current frame  201  and task  250  handles the processing of the stored signal. Task  270  handles the extraction of signaling information from the signal received during the current frame.  
         [0031]    The signal reception task  200  is initiated for every frame upon the raw signal being converted to a digital signal. At block  202 , the digitally converted signal is received. At block  204 , the received signal is stored in RAM  212  prior to the de-spreading of the signal. When storing the signal in RAM  212 , the master controller uses the first buffer  114  and the second buffer  116 . In the preferred embodiment, for every frame, master controller  130  toggles the use between the first buffer  114  and the second buffer  116  when storing the received signal. For example, in any given frame the master controller  130  may read from the first buffer  114  and write in the second buffer  116 , then toggle for the next frame such that master controller  130  is now reading from the second frame  116  and writing in the first frame  114 .  
         [0032]    The signal-processing task  250  is initiated for every frame upon start of each frame. At block  252 , the master controller  130  replays the signal stored in the previous frame (also referred to as, previous frame signal) and processes the stored signal using the signaling information received from the conventional rake receiver  118 . At block  256 , using the signaling information, the master controller  130  determines if there is a data packet for this mobile station on any of the shared supplemental channels. If yes, then at block  258 , the master controller  130  de-spreads the stored signal using signaling information, such as the Walsh codes and other information. Thereafter, the master controller  130  processes the control channel, the supplemental channel and decodes the data using the signaling information.  
         [0033]    The signaling information extraction tasks  270  is initiated for every frame upon the raw signal being converted to a digital signal. At block  272 , the rake receiver  118 , using well-known techniques, generally defined in the standards, extracts the signaling information from the dedicated channel of the current frame signal. At block  274 , the rake receiver provides the signaling information to the master controller  130 .  
         [0034]    [0034]FIG. 3 shows a mobile station  300  according to a second embodiment of the present invention. In this Figure, components, which are similar to those described with reference to FIG. 1, have been numbered with like reference numerals. In addition to the components described in the mobile station  104 , the mobile station  300  according the second embodiment, further comprises a control channel decoder  302 . The control channel decoder is coupled to the analog to digital (A2D) converter  110  and master controller  330 . In an operation according to the second embodiment, the A2D converter  110  sends the converted signal to the control channel decoder  302 , the Rake receiver  118  and stores the signal in RAM  112 . The control channel  302  processes the control channel of the received signal and provides the information to master controller  330  to use during next frame processing. Simultaneously, the Rake receiver  118  processes the received signal to extract signaling information of the current frame. In the second embodiment, the master controller  330 , uses the signaling information from Rake receiver  118  to determine is the there is any data packets for this mobile station.  
         [0035]    The operations of the master controller  330  are similar to that described for master controller  130 , except for the following. Since master controller  330  receives the control channel information from the control channel decoder  302 , the master controller  330  does not process the control channel. At the start of the frame the master controller  330  replays signal and de-spreads the supplement channels to extract the data packets. The data packets are processed according to proposed standards. This embodiment offers an advantage of faster data packet processing, since the control channel decoder  302  processes the control channel information in the previous frame which is used by the master controller  330 .  
         [0036]    [0036]FIG. 4 illustrates flowcharts of tasks according to the second embodiment, generally shown as  200 ,  270 ,  450  and  480 , which are executed simultaneously during each frame. In this Figure, tasks, which are similar to those described with reference to FIG. 2, have been numbered with like reference numerals (for example tasks  200  and  270 ).  
         [0037]    In the second embodiment of the invention the master controller  130  simultaneously executes tasks,  200  and  450 . The Rake receiver  118  executes task  270  and the control channel decoder  302  executes task  480 . As described in FIG. 2, task  200  handles the reception of the communication signal during the current frame  201  and task  270  handles the extraction of signaling information from the signal received during the current frame. Task  450  handles the processing of the stored signal and task  480  handles the processing of the control channel.  
         [0038]    The signal-processing task  450  is initiated for every frame upon start of each frame. At block  452 , the master controller  130  replays the signal stored in the previous frame and processes the stored signal using the signaling information received from the conventional rake receiver  118 . At block  456 , using the signaling information, the master controller  330  determines if there is a data packet for this mobile station on any of the shared supplemental channels. If yes, then at block  458 , the master controller  330  de-spreads the stored signal using signaling information, such as the Walsh codes and other information. Thereafter, the master controller  330  processes the supplemental channel and decodes the data using the signaling information.  
         [0039]    The control channel-decoding task  480  is initiated for every frame upon the raw signal being converted to a digital signal. At block  482 , the control channel decoder  302 , decodes the received signal of the current frame to process the control channel information. At block  484 , the control channel information is sent to the master controller  330 .  
         [0040]    While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. That is, other modifications and variations to the invention will be apparent to those skilled in the art from the foregoing disclosure and teachings. Thus, while only certain embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention.