Abstract:
The invention provides a method and apparatus for transmitting signalling information to a receiver using a plurality of transmission antennas in a time switching configuration. The apparatus includes a controller for generating a switch controlling signal in a non-overlapped time cycle for selecting one of the plurality of transmission antennas to output a transmission signal in a fixed, non-overlapped time interval. The invention further provides for a receiving device for detecting a pilot channel signal from an input forward link signal and generating estimated phase and time values for detecting a traffic channel signal at the selected estimated time position and correcting a phase error of the detected traffic channel signal based on the estimated phase value, for signal decoding.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the field of communication systems, and particularly to a method and apparatus for transmitting/receiving data with a time switched transmission diversity (TSTD) function. 
   2. Description of the Related Art 
   In a mobile communication system, data transmission/reception performance can generally be enhanced by utilizing diversity techniques in a fading environment. Typically, as shown in  FIG. 1  three diversity techniques are applicable to the forward link and a single diversity technique (i.e., receiver diversity) is applicable to the reverse link. Data can be received on the reverse link with receiver diversity by equipping a base station with a plurality of reception antennas. For the forward link, the three well known diversity techniques include transmission diversity, receiver diversity, and mixed diversity. In transmission diversity, a base station transmits a signal through a plurality of transmission antennas and a mobile station receives the signal through a single reception antenna to achieve the same effect as if multiple reception antennas were used. Receiver diversity is provided when the mobile station has a plurality of reception antennas, and mixed diversity is defined as a combination of the two aforementioned techniques. 
   Receiver diversity on the forward link, however, is problematic in that diversity gain is low because of the small terminal size which limits the distance between reception antennas. Another problem is that the use of multiple reception antennas requires a separately procured hardware configuration for receiving a forward link signal and transmitting a reverse link signal through a corresponding antenna, thereby imposing constraints on the size and cost of the terminal. In view of these problems, mobile communication systems typically employ transmission diversity exclusively on the forward link. 
     FIG. 2  illustrates a general block diagram of a mobile communication system employing transmission diversity on a forward link. A base station  100  and a mobile station  200  include transmitting and receiving apparatus, respectively. A baseband signal processor  103  of base station  100  converts user data for transmission on the forward link into a baseband signal. Such conversion by baseband signal processor  103  includes channel encoding, interleaving, orthogonal modulation, and PN (Pseudo Noise) spreading. A signal distributor  102  distributes the signals received from the baseband signal processor  103  into N signal streams with each stream being provided to one of N transmission antennas TXAI to TXAN. As a result, transmission diversity is achieved at the transmission end of the base station  100  through the N antennas. 
   The mobile station  200  has a single reception antenna RXA for receiving signals from the base station  100  from the N transmission antennas. To process the received signals, the mobile station  200  includes N demodulators  201  to  20 N corresponding to each N transmission antenna. A combiner  211  combines demodulated signals received from the demodulators  201  to  20 N, and a decoder &amp; controller  213  decodes a signal received from the combiner  211  to produce decoded user data. 
   In contrast, the structure of a transmitter in a non-transmission diversity (NTD) CDMA communication system is described with reference to  FIG. 3. A  base station  300  includes a CRC (Cyclic Redundancy Check) generator  311  for adding CRC bits to input user data in order to detect a frame error which occurs while sending the user data. A tail bit generator  313  adds tail bits indicating termination of a data frame to the data frame prior to channel encoding. Then, a channel encoder  315  encodes the data frame for error correction and an interleaver  317  interleaves the encoded data. A combiner  323  performs an exclusive-OR operation on the interleaved data with a long code sequence. This long code sequence is generated in a long code generator  319  and decimated in a decimator  321  at the same rate as that at the output terminal of the interleaver  317 . A signal mapper  325  converts 0s and 1s of the encoded data received from the combiner  323  to +1s and −1s respectively, for orthogonal modulation. A serial-to-parallel (S/P) converter  327  divides the signal received from the signal mapper  325  into I channel and Q channel streams, for QPSK (Quadrature Phase Shift Keying) modulation. The I channel and Q channel streams are subject to orthogonal modulation in multipliers  329  and  331  and PN spreading in a PN spreader  333 . The spread signals are filtered for pulse shaping in LPFs (Low Pass Filters)  335  and  337 , loaded on a carrier by mixers  339 ,  341 , combined with combiner  343 , and finally transmitted through a transmission antenna. 
   The transmit signal which is output from the NTD transmitter in the base station  300  illustrated in  FIG. 3  has a signal structure indicated by  511  of FIG.  5 . Specifically,  FIG. 5  illustrates timing characteristics for the case of transmitter diversity and no diversity. Specifically in the case of no diversity,  FIG. 5  illustrates user data output from the NTD  511  transmitter, and for the diversity case.  FIG. 5  further illustrates timing characterization from an orthogonal transmission diversity (OTD) transmitter with two antennas, A &amp; B (N=2). 
     FIG. 4  is a block diagram of an OTD transmitter with two transmission antennas (N=2). Improved performance of a forward link is achieved in the OTD transmitter by dividing information for one user into two or more streams and transmitting the divided data through the plurality of transmission antennas, as indicated by  513  and  515  of FIG.  5 . The following description is conducted with the understanding that [W m −W m ] is identical to [W m {overscore (W m )}]. 
   The OTD transmitter, illustrated in  FIG. 4 , operates in the same manner as the NTD transmitter of  FIG. 3 , except for a serial-to-parallel conversion process. In the OTD structure, mapped data branches into N streams, corresponding to the number of transmission antennas in S/P converters  413 ,  415 , and  417 , and orthogonally modulated in multipliers  419 ,  421 ,  423 , and  425 , for maintaining mutual orthogonality between the transmission antennas. 
   In addition to orthogonal modulation, orthogonal codes may be further utilized to ensure mutual orthogonality among the N antennas. The orthogonal code extension is accomplished by a Hadamard matrix extension. In the case of the OTD transmitter with two transmission antennas A and B(i.e., A and B as shown in  FIG. 4 ) the different orthogonal codes assigned to the antennas are respectively [W m W m ] and [W m −W m ], extended from an orthogonal code W m  of a length 2 m  used in the NTD transmitter. The purpose of orthogonal code extension is to compensate for the data rate of each of the N streams, which is 1/N of the data rate prior to serial-to-parallel conversion. 
   A receiver for receiving a signal from the OTD transmitter requires signal demodulators for demodulating user data, a pilot demodulator for providing timing and phase information to be provided to the signal demodulates, and a parallel-to-serial (P/S) converter for converting M signal demodulator outputs to a serial signal stream. 
   A pilot channel is used by the base station to provide timing and phase information to a mobile station. The mobile station first activates the pilot demodulator to acquire necessary timing and phase information and demodulates user data based on the acquired information. For an OTD transmitter, each transmission antenna should be assigned a unique pilot channel. 
   In a receiver for use with a conventional OTD transmitter of  FIG. 4 , the pilot demodulator subjects a received signal to PN despreading and orthogonal demodulation and integrates the resulting signal for one cycle in order to demodulate a pilot channel from the received signal. A time estimator and a phase estimator in the pilot demodulator estimate timing and phase values from the integrated value. 
   A signal demodulator of the receiver performs PN despreading on a user data signal based on timing information received from the pilot demodulator. A phase error which occurs during transmission is compensated for by multiplying the phase information by an integrated value. The integrated value is obtained by integrating an orthogonally modulated signal for one cycle. The phase-compensated integrator output is converted to a probability value by a soft decision block and fed through the P/S converter to a deinterleaver. 
   Despite improved reception performance as compared to the NTD system, the conventional OTD mobile communication system has certain limitations. First, given that a terminal should be equipped with a number of pilot demodulators and signal demodulators corresponding to the number of transmission antennas of a base station, this results in an increase in the complexity, cost, and power consumption of a receiver. 
   Another drawback associated with a conventional OTD system is that the length of an orthogonal code used is increased by N times from that of an NTD case, for N transmission antennas. As a result, the integration interval is extended, thereby degrading reception performance in a frequency error-susceptible channel environment. 
   A further limitation is that the number of available transmission antennas is restricted to be a power of 2, namely 2 n  which imposes constraints concerning a number of applications involving antenna arrays. There exists a need, therefore, for a diversity scheme which overcomes the limitations of the prior art. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a time switched transmission diversity (TSTD) apparatus and method for distributing a signal of a base station to a plurality of antennas via time switching. 
   Another object of the present invention is to provide a receiver for receiving a signal from a TSTD transmitter. 
   A further object of the present invention is to provide a TSTD communication apparatus and method in a mobile communication system, in which the length of an orthogonal code remains the same as that required in a conventional mobile communication system. 
   Still another object of the present invention is to provide a receiver and a receiving method in a TSTD mobile communication system, in which a single signal demodulator is utilized irrespective of the number of transmission antennas employed to achieve transmission diversity. 
   A still further object of the present invention is to provide a transmitter and a transmitting method in a TSTD mobile communication system, where the number of transmission antennas can be easily increased. 
   According to one aspect of the present invention, the above objects are achieved by providing a time diversity transmitting apparatus in a base station of a mobile communication system. The transmitting apparatus includes a plurality (N) of transmission antennas with a corresponding number of radio frequency transmitters connected therewith for outputting signals on a forward link. The transmitter further includes a controller for generating a switch controlling signal in a non-overlapped time cycle, an orthogonal modulator for modulating a transmit signal by an orthogonal code, a spreader for spreading the output of the orthogonal modulator, and a switch connected to an output terminal of the spreader, for connecting the output of the spreader to a corresponding transmitter based on the switch controlling signal. 
   According to another aspect of the present invention, there is provided a receiving device in a mobile station of a mobile communication system. The receiving device has a pilot channel receiver for detecting a pilot channel signal from an input forward link signal and generating estimated phase and time values, a controller for generating a selection control signal based on cycle information and switching pattern information, in synchronization of a reference time to a base station, a selector for selectively outputting the estimated phase and time values received from the pilot channel receiver based on the selection control signal, and a traffic channel receiver for detecting a traffic channel signal at the selected estimated time position and correcting a phase error of the detected traffic channel signal based on the estimated phase value, for signal decoding. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  illustrates diversity techniques on forward and reverse links in a mobile communication system; 
       FIG. 2  is a block diagram of a transmission diversity-based apparatus on a forward link in a mobile communication system according to the present invention; 
       FIG. 3  is a block diagram of an NTD transmitter in a mobile communication system according to the prior art; 
       FIG. 4  is a block diagram of a conventional OTD transmitter in a mobile communication system according to the prior art; 
       FIG. 5  illustrates data structures transmitted from the NTD and OTD transmitters shown in  FIGS. 3 and 4 , respectively; 
       FIG. 6  is a block diagram of a TSTD transmitter in a mobile communication system according to an embodiment of the present invention; 
       FIG. 7  is a block diagram of a controller shown in  FIG. 6 ; 
       FIG. 8  illustrates timing characteristics of data transmitted in a periodic pattern from the TSTD transmitter of  FIG. 6 ; 
       FIG. 9  illustrates timing characteristics of data transmitted in a random pattern from the TSTD transmitter of  FIG. 6 ; 
       FIG. 10  illustrates timing characteristics of data for plural users synchronously transmitted from the TSTD transmitter of  FIG. 6 ; 
       FIG. 11  illustrates timing characteristics of data for a plurality of users asynchronously transmitted from the TSTD transmitter of  FIG. 6 ; 
       FIG. 12  describes transmission antenna extensibility in a TSTD transmitter of the mobile communication system according to the embodiment of the present invention; 
       FIG. 13  is a block diagram of an embodiment of a receiving device for receiving data from a TSTD transmitting device in the mobile communication system according to the present invention; and 
       FIG. 14  is a block diagram of another embodiment of a receiving device for receiving data from a TSTD transmitting device in the mobile communication system according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A mobile communication system according to an embodiment of the present invention distributes user data to a plurality of transmission antennas by time switching to achieve transmission diversity. The system further demodulates the time diversity-based signal in a single signal demodulator. The features of time diversity according to the present invention may be summarized as:
         (1) A single signal demodulator is provided for demodulating user data regardless of the number N of transmission antennas utilized. That is, only one orthogonal code is available per user. As such, the single demodulator simplifies the receiver design, accommodates low power dissipation and results in low terminal costs;   (2) The length of an orthogonal code is the same as that of an orthogonal code used in an NTD device, regardless of the number N of transmission antennas. This implies that there is no increase of an integration interval for providing time diversity; and   (3) The number of available transmission antennas is not restricted to be a power of 2, 2 n  but is limitlessly extensible, thereby imposing no constraints on other applications.       

   Prior to describing the structure and operation of a transmitter in a base station and a receiver in a terminal according to the embodiment of the present invention, it is to be noted that the method of time diversity in accordance with the present invention is applied to the forward link in a mobile communication system of the present invention. 
     FIG. 6  is a block diagram of a TSTD transmitter with two (N=2) transmission antennas in a base station according to the present invention. 
   Referring to  FIG. 6 , a signal mapper  611  receives a signal resulting from combining encoded user data with a long code whereby the long code changes the level of the received signal by converting 0s and 1s to +1s and −1s, respectively. An S/P converter  613 , coupled to the signal mapper output, converts a serial signal received from the signal mapper  611  to an odd-numbered signal and an even-numbered signal. A multiplier  615 , coupled to the even output of the S/P converter, multiplies the even-numbered signal by an orthogonal code W m . A multiplier  617 , coupled to the odd output of the S/P converter, multiplies the odd-numbered signal by an orthogonal code W m . These multipliers  615  and  617  function to subject a user signal to orthogonal modulation (i.e., orthogonal spreading) by multiplication. The orthogonal code can be a Walsh code. A PN spreader  619  multiplies the orthogonally modulated signals received from the multipliers  615  and  617  by corresponding PN sequences PN I  and PN Q , for PN spreading (or PN masking) of a signal to be transmitted. 
   A controller  600  generates a switch controlling signal for distributing a transmit signal to a plurality of antennas in the TSTD transmitter of the present invention. The controller  600  synchronizes to a GPS (Global Positioning System) signal in a synchronous mode and a switching cycle is an integer multiple of the orthogonal code length. In addition, a look-up table for storing switching information with respect to a hopping pattern may be provided to the controller  600  in an alternate embodiment whereby time switching is performed in a specific pattern. 
   A switch  621  switches in response to a switch controlling signal output by the controller  600 , and has a common terminal coupled to output terminals of the PN spreader  619  from which I channel and Q channel spread signals are transmitted, a first output terminal coupled to LPFs  623  and  625 , and a second output terminal coupled to LPFs  627  and  629 . As previously stated, the switch  621  switches based on a switch controlling signal received from the controller  600  and selectively outputs the spread signals received from the PN spreader  619  to the low pass filters LPFs  623  and  625  or to the LPFs  627  and  629 . 
   The LPFs  623  and  625  low-pass-filter the I channel and Q channel PN spread signals received from the switch  621 . Multipliers  631  and  633  multiply outputs of the LPFs  623  and  625  by carriers, for frequency up conversion. An adder  641  adds signals received from the multipliers  631  and  633  and sends the resulting signal to a transmission antenna A. 
   The LPFs  627  and  629  low-pass-filter the I channel and Q channel PN spread signals received from the switch  621 . Multipliers  635  and  637  multiply outputs of the LPFs  627  and  629  by carriers, for frequency up conversion. An adder  643  adds signals received from the multipliers  631  and  633  and sends the resulting signal to a transmission antenna B. 
   The structure shown in  FIG. 6  can be adapted as a forward channel transmitter in the TSTD base station. Forward channel transmitters include a pilot channel transmitter, a sync channel transmitter, a control channel transmitter, and a traffic channel transmitter. Considering that a pilot channel provides time synchronization for transmission of data on a forward link, the pilot channel transmitter can be configured to be an OTD structure, while the other channel transmitters can use the TSTD structure shown in FIG.  6 . 
     FIG. 7  is a block diagram of the controller  600  shown in FIG.  6 . Referring to  FIG. 7 , a reference cycle register  711  stores a reference cycle signal received from an upper-level processor. The reference cycle signal acts as a time switching cycle in a channel transmitter. A clock counter  713  receives clock pulses from a base station system, counts the clock pulses in a reference cycle unit, and generates read pulses. A look-up table  715  stores switching pattern information received from the upper-level processor and outputs corresponding switching information in response to the read pulses received from the clock counter  713 . A control signal generator  717  generates a switch controlling signal for distributing a PN spread signal to a plurality of transmission antennas according to the pattern information read from the look-up table  715 . 
   By way of example, the controller  600  of  FIG. 7  functions to connect a baseband output to N antennas for transmission in successive time intervals in a TSTD base station transmitter. The reference cycle register  711  stores a time switching cycle for a channel so that each channel can be uniquely time-switched. That is, designating a different reference cycle signal for each channel in the reference cycle register  711  results in transmission of each channel at a unique switching cycle rate. The value stored in the reference cycle register  711  is designated separately for each channel in the upper-level processor prior to transmission of the channel, and can be changed during data transmission under a separately determined control. 
   The clock pulses input to the clock counter  713  are provided from the base station system, synchronized to a reference time in the base station, and have a clock cycle proportional to an orthogonal code length. The clock counter  713  counts the clock pulses, compares the counted value with the value stored in the reference cycle register  711 , and sends read pulses to the look-up table  715  at the time point when the values are equal. 
   The look-up table  715  is a memory for storing a time switching pattern of data transmitted through the N transmission antennas. A different switching pattern can be assigned to each channel, or channels can share the same switching pattern. The switching pattern stored in the look-up table  715  is to be transmitted from the base station to the terminal to allow the terminal to demodulate data based on the switching pattern. 
   The control signal generator  717  analyzes the switching pattern read from the look-up table  715  and controls signal paths to the N transmission antennas. That is, only one selected transmission antenna is enabled and the other transmission antennas are disabled. 
   In summary, the controller  600  counts input clock pulses, compares the counted value with a reference cycle value, and generates a read signal corresponding to a switching pattern stored in the look-up table  715  if the values are equal. The switching pattern information is used to select a transmission antenna in a subsequent step. The thus-obtained switching information is changed to an enable/disable signal for each transmission path. 
     FIG. 8  illustrates a comparison between signal characteristics transmitted from a conventional NTD transmitter and the TSTD transmitter of the present invention shown in FIG.  6 . In  FIG. 8 , reference numeral  811  illustrates an output timing of an NTD transmitter. Reference numerals  813  and  815  illustrate the timings of signals respectively transmitted through transmission antennas A and B in the TSTD transmitter. It is apparent that only one antenna is active (i.e., A or B) at any point in time in accordance with the teachings of the present invention. 
   In operation, the TSTD transmitter uses one orthogonal code per user, as compared to an OTD transmitter requiring as many orthogonal codes as there are transmission antennas. Further, the OTD transmitter operates in the same manner as the NTD transmitter, up to PN spreading. Then, for an TSTD transmitter the PN spread data is switched to each transmission antenna in a cycle equal to an integer multiple of an orthogonal code length, either in a periodic pattern for sequential data transmission to the N transmission antennas or in a random pattern. The time switching pattern used is determined by the output of the look-up table  715  in the controller  600 , and a time switching cycle is determined by a reference cycle value stored in the reference cycle register  711 . 
     FIG. 9  illustrates, by way of example, a random transmission pattern from two antennas (i.e., A and B), while  FIG. 8  illustrates a periodic pattern for antennas A and B. With reference to  FIG. 9 , look-up table  715  would be loaded, for example, with a switching pattern requiring that data should be connected to the transmission antenna A for two consecutive iterations and then to transmission antenna B once in the TSTD transmitter of FIG.  6 . In response, the controller  600  control the switch  621  to connect the output of the PN spreader  619  to the LPFs  623  and  625  for two consecutive switching cycles and to the LPFs  627  and  629  for one subsequent switching cycle. As a result, the timings of signals output from the transmission antennas A and B are shown as indicated by  913  and  915  of  FIG. 9 , respectively. Random time switching patterns can additionally offer the data scrambling effect. 
     FIG. 10  is a timing diagram of user data under the following conditions: N=2, two users, and synchronous time switching in the TSTD transmitter of a base station. 
     FIG. 11  is a timing diagram of user data under the following condition: N=2, two users, and asynchronous time switching in the TSTD transmitter. Synchronous time switching is distinguishable from asynchronous time switching depending upon whether the same or different time switching schemes are applied to all terminals for a base station. 
     FIG. 12  is a timing diagram comparing user data transmitted from a TSTD transmitter and the OTD transmitter. In  FIG. 12 , N=3 and a periodic pattern is selected. As illustrated, the TSTD transmitter exhibits time diversity with three transmission antennas. This result is not obtainable in the OTD case. 
   Two types of receiving devices may be used for a terminal corresponding to a TSTD transmitting device. In one type, OTD is applied to a pilot channel and TSTD to all other channels. In the second type, TSTD is applied to all channels including the pilot channel and user data channels. 
     FIGS. 13 and 14  are block diagrams of the two types of receiving devices. Because the pilot channel is a common channel for synchronizing the PN code between the base station and the terminal. Either OTD or TSTD with a predetermined cycle and pattern can be rendered to transmission of the pilot channel. 
     FIG. 13  is a block diagram of a receiving device for receiving a baseband signal from a transmitting device having two transmission antennas, a TSTD traffic channel transmitter, and an OTD pilot channel transmitter. Referring to  FIG. 13 , the receiver includes a number of pilot channel receivers equal to the number of transmission antennas of the transmitting device. Specifically, two pilot channel receivers  1310  and  1320  are provided corresponding to transmission antennas A and B. The pilot channel receivers should preferably use orthogonal codes extended in length, proportional to the number of the transmission antennas. 
   In the pilot channel receiver  1310 , a PN despreader  1311  multiplies an input signal by a PN sequence, for PN despreading. A multiplier  1313  orthogonally demodulates the signal received from the PN despreader  1311  by multiplying the received signal by the same orthogonal code [W m  W m ] as the one used in the pilot channel transmitter. An integrator  1315  integrates a signal received from the multiplier  1311  for a time T and sums the integrated values. A phase estimator  1317  analyzes a signal received from the integrator  1315  and outputs an estimated phase value 0 of the pilot signal received through the transmission antenna A. A time estimator  1319  analyzes the signal received from the integrator  1315  and outputs an estimated time value 0 as the transmission time of the pilot signal received through the transmission antenna A. The time estimator  1319  outputs an estimated time value 1 as the transmission time of the pilot signal received through the transmission antenna B. 
   In the pilot channel receiver  1320 , a PN despreader  1321  multiplies the input signal by a PN sequence, for PN despreading. A multiplier  1323  orthogonally demodulates the signal received from the PN despreader  1321  by multiplying the received signal by the same orthogonal code [W m {overscore (W m )}] as the other used in the pilot channel transmitter. An integrator  1325  integrates a signal received from the multiplier  1321  for a time T and sums the integrated values. A phase estimator  1327  analyses a signal received from the integrator  1325  and outputs an estimated phase value 1 of the pilot signal received through the transmission antenna B. A time estimator  1329  analyses the signal received from the integrator  1325  and outputs an estimated time value 1 as the transmission time of the pilot signal received through the transmission antenna B. 
   A controller  1341  synchronizes to a reference time of the base station and generates a control signal for selecting the outputs of the pilot channel receivers  1310  and  1320  in a time switching cycle unit. A selector  1343  selectively outputs the estimated phase and time values received from the pilot channel receivers  1310  and  1320  on the basis of the control signal of the controller  1341 . 
   In a traffic channel receiver  1330 , a PN despreader  1331  multiplies an input signal at a transmission time position indicated by the time signal received from the selector  1343  by a PN sequence. That is, the PN despreader  1331  despreads the input signal by the PN code at the estimated switching time position. A multiplier  1333  multiplies the orthogonal code [W n ] used in the traffic channel transmitter by a signal received from the PN despreader  1331 . An integrator  1335  integrates a signal received from the multiplier  1333  for the time T and sums the integrated values. A phase sign converter  1345  changes the sign of the phase value received from the selector  1343 . A multiplier  1337  multiplies the output of the integrator  1335  by the output of the phase sign converter  1345 , to synchronize the phase of the input signal. A level decision block  1339  detects the level of a signal received from the multiplier  1337  and changes the signal level to a gray level. The signal output from the level decision block  1339  is fed to a decoder in the receiver. 
   The receiving device shown in  FIG. 13  includes pilot channel demodulators equal to the number of transmission antennas employed, N. In the present example, N=Z. These pilot channel receivers are similarly configured as the OTD receivers and operate in the same manner. A single traffic channel receiver  1330  is all that is required because even though modulation of user data is distributed to N transmission antennas, each of the n data paths use the same orthogonal code. 
   The estimated time and phase information for the N transmission antennas is selectively provided from the pilot channel receivers  1310  and  1320  to the traffic channel receiver  1330  by the selector  1343  based on the clock signal of the controller  1341  synchronized to the base station. That is, the terminal obtains switching cycle and pattern information from the base station during a call set-up. 
   The controller  1341  obtains the information pertaining to the current selected switching scheme by demodulating a sync channel based on time and phase information pilot obtained from a demodulated pilot channel and analyzing information loaded on the demodulated sync channel. Upon detection of the switching scheme for TSTD in a receiving device, the terminal can be synchronized to the base station for time switching. 
   The traffic channel receiver  1330  subjects a user data signal to PN despreading using the estimated time value selectively received from the selector  1343  and orthogonally demodulates the PN spread signal. Then, it integrates the orthogonal modulation signal for one cycle, and multiplies the integrated value by a value obtained from converting the sign of phase information selected by the selector  1343 , to thereby compensate for a phase error which occurs during data transmission. The phase-compensated integrator output is subjected to soft decision and converted to a probability value in the level decision block  1339  and fed through a P/S converter (not shown) to a deinterleaver (not shown). 
     FIG. 14  is a block diagram of another embodiment of a receiving device for receiving a signal from a transmitting device having a TSTD structure for all channel transmitters. The receiving device in this embodiment includes a single pilot channel receiver since a pilot channel signal is also time switched for transmission. 
   In a pilot channel receiver  1410 , a PN despreader  1411  multiplies an input signal by a PN sequence, for PN despreading. A multiplier  1413  orthogonally demodulates the signal received from the PN despreader  1411  by multiplying the received signal by the same orthogonal code W m  as that used in a corresponding pilot channel transmitter. An integrator  1415  integrates a signal received from the multiplier  1411  for a time T and sums the integrated values. A phase estimator  1417  analyses a signal received from the integrator  1415  and outputs an estimated phase value of a pilot channel signal received through transmission antennas. A time estimator  1419  analyzes the signal received from the integrator  1415  and outputs an estimated time value as the transmission time of the pilot channel signal received through the transmission antennas. 
   A controller  1441  synchronizes to a reference time of the base station and generates a control signal for selecting the outputs of the pilot channel receiver  1410  in a time switching cycle unit. A selector  1443  selectively outputs the estimated phase and time values received from the pilot channel receiver  1410  on the basis of the control signal of the controller  1441 . 
   In a traffic channel receiver  1420 , a PN despreader  1421  multiplies an input signal at a time position indicated by the time signal received from the selector  1343  by a PN sequence. That is, the PN despreader  1421  despreads the input signal by the PN code at the estimated switching time position. A multiplier  1423  multiplies the orthogonal code [W n ] used in a corresponding traffic channel transmitter by a signal received from the PN despreader  1421 . An integrator  1425  integrates a signal received from the multiplier  1423  for the time T and sums the integrated values. A phase sign converter  1431  changes the sign of the phase value received from the selector  1443 . A multiplier  1427  multiplies the output of the integrator  1425  by the output of the phase sign converter  1431 , to synchronize the phase of the input signal. A level decision block  1429  detects the level of a signal received from the multiplier  1427  and changes the signal level to a gray level. The signal output from the level decision block  1429  is fed to a decoder in the receiver. 
   The receiving device shown in  FIG. 14  shows an example where TSTD is executed on a pilot channel as well as traffic channels. Since one orthogonal code is used for the pilot channel, which differs from the receiving device of  FIG. 13 , all necessary timings and estimated phases can be generated by the use of the single pilot channel receiver  1410  with implementation of the same time switching technique as that for the traffic channel receiver  1420 . 
   In summary, TSTD on a forward link in a mobile communication system offers the following advantages:
         (1) only one traffic channel receiver is needed for demodulating user data regardless of the number N of transmission antennas, since one orthogonal code is available per user, which enables simplification of a receiver, low power dissipation and low terminal costs;   (2) The length of an orthogonal code is unchanged by virtue of using the orthogonal code in an NTD device. Therefore, there is no increase of an integration interval for providing time diversity and no degradation of the reception performance possibly caused by a channel environment such as a frequency error;   (3) The number of available transmission antennas is not limited, thereby imposing no constraints on other applications; and   (4) A scrambling effect can be added to improvement in reception performance by applying different switching techniques to users in a base station.       

   While the present invention has been described in detail with reference to the specific embodiments, they are mere exemplary applications. Thus, it is to be clearly understood that many variations can be made by anyone skilled in the art within the scope and spirit of the present invention.