Abstract:
A method of transmitting signals in a communication system over at least two time periods including generating a base signal comprising of at least two samples in each time period, selecting a scrambling sequence of length equal to or greater than the number of time periods, scaling all samples in said signal in a time period with one element of said scrambling sequence and transmitting the scaled signal in said time period. Different elements of the scrambling sequence are used to scale the base signal in different time periods. The signal in each time period is obtained by scaling a base signal. The scrambling sequence is preferably a pseudo-random sequence. The step of scaling all samples in said signal in a time period consists of multiplying all samples of said signal with an element of said scrambling sequence.

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 U.S.C. 119(e)(1) to U.S. Provisional Application No. 60/910,126 filed Apr. 4, 2007. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The technical field of this invention is wireless telephone communication, particularly Evolved-UMTS Radio Access (E-UTRA) communication. 
     BACKGROUND OF THE INVENTION 
     As wireless systems proliferate, the expanding user base and the demand for new services necessitate the development of technologies capable of meeting users&#39; ever increasing expectations. Users of mobile telecommunications devices expect not only globally available reliable voice communications but a variety of data services, such as email, text messaging and internet access. 
     SUMMARY OF THE INVENTION 
     A method of transmitting signals in a communication system over at least two time periods including generating a base signal comprising of at least two samples in each time period, selecting a scrambling sequence of length equal to or greater than the number of time periods, scaling all samples in the signal in a time period with one element of the scrambling sequence and transmitting the scaled signal in the time period. Different elements of the scrambling sequence scale the base signal in different time periods. The signal in each time period is obtained by scaling a base signal. The scrambling sequence is preferably a pseudo-random sequence. The step of scaling all samples in the signal in a time period consists of multiplying all samples of the signal with an element of the scrambling sequence. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of this invention are illustrated in the drawings, in which: 
         FIG. 1  is a diagram of a communication system of the present invention having three cells; 
         FIG. 2  is a block diagram of a first embodiment of a modulation block suitable for use in this invention; 
         FIG. 3  is a block diagram of a second embodiment of a modulation block suitable for use in this invention; 
         FIG. 4  is a schematic view of orthogonal frequency division multiplexing time slots; 
         FIG. 5  is a schematic view of block spreading processing in orthogonal frequency division multiplexing time slots; 
         FIG. 6  is a schematic view of a first embodiment of combined block scrambling and block spreading processing in orthogonal frequency division multiplexing time slots according to this invention; 
         FIG. 7  is a schematic view of a second embodiment of combined block scrambling and block spreading processing in orthogonal frequency division multiplexing time slots according to this invention; 
         FIG. 8  is a schematic view of a third embodiment of combined block scrambling and block spreading processing in orthogonal frequency division multiplexing time slots according to this invention; and 
         FIG. 9  is a flow chart illustrating the steps of this invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an exemplary wireless telecommunications network  100 . The illustrative telecommunications network includes base stations  101 ,  102  and  103 , though in operation, a telecommunications network necessarily includes many more base stations. Each of base stations  101 ,  102  and  103  are operable over corresponding coverage areas  104 ,  105  and  106 . Each base station&#39;s coverage area is further divided into cells. In the illustrated network, each base station&#39;s coverage area is divided into three cells. Handset or other user equipment (UE)  109  is shown in Cell A  108 . Cell A  108  is within coverage area  104  of base station  101 . Base station  101  transmits to and receives transmissions from UE  109 . As UE  109  moves out of Cell A  108  and into Cell B  107 , UE  109  may be handed over to base station  102 . Because UE  109  is synchronized with base station  101 , UE  109  can employ non-synchronized random access to initiate handover to base station  102 . 
     Non-synchronized UE  109  also employs non-synchronous random access to request allocation of up-link  111  time or frequency or code resources. If UE  109  has data ready for transmission, which may be traffic data, measurements report, tracking area update, UE  109  can transmit a random access signal on up-link  111 . The random access signal notifies base station  101  that UE  109  requires up-link resources to transmit the UE&#39;s data. Base station  101  responds by transmitting to UE  109  via down-link  110 , a message containing the parameters of the resources allocated for UE  109  up-link transmission along with a possible timing error correction. After receiving the resource allocation and a possible timing advance message transmitted on down-link  110  by base station  101 , UE  109  optionally adjusts its transmit timing and transmits the data on up-link  111  employing the allotted resources during the prescribed time interval. 
       FIG. 2  illustrates a block diagram of the modulation of an orthogonal frequency-division multiplexed access (OFDMA) system. Block [c k ( 0 ) . . . c k (L−1)]  201  denotes the user signal of user k. This user signal includes but not limited to reference signal, data signal, control signal, and random access pre-amble. Modulation block  210  includes tone map  211 , inverse Fast Fourier transform (IFFT) block  212  and parallel-to-serial (P/S) converter  213 . Tone map  211  maps the user signal onto L sub-carriers in the frequency domain. IFFT block  212  converts these signals from frequency domain to temporal domain.  FIG. 2  contemplates that modulator  210  services a plurality of UEs. The plural signals from the plural UEs are transmitted on different sub-carriers at the same time period as designated by a UE specific tone map. These plural user signals and tone maps  211  are omitted for clarity. P/S converter  213  converts these parallel signals into a single serial signal. Block  220  inserts a cyclic prefix (CP)  221  to be transmitted with the data  222 . 
       FIG. 3  illustrates an alternate modulation to that of  FIG. 2 . Block [c k ( 0 ) . . . c k (L−1)]  201  denotes the user signal of user k. This user signal includes but not limited to reference signal, data signal and control signal. Modulation block  310  includes discrete Fourier Transform (DFT) block  311 , tone map  312 , inverse Fast Fourier transform (IFFT) block  313  and parallel-to-serial (P/S) converter  314 . In  FIG. 3 , the user signal is first processed by DFT block  311 . Tone map  312  maps the user signal onto L sub-carriers as described above in conjunction with  FIG. 2 . IFFT block  313  converts these signals from frequency domain to temporal domain.  FIG. 3  contemplates that modulator  310  services a plurality of UEs. The plural signals from the plural UEs are transmitted on different sub-carriers at the same time period as designated by a UE specific tone map. These plural user signals, DFT blocks  311  and tone maps  312  are omitted for clarity. P/S converter  314  converts these parallel signals into a single serial signal. Block  220  inserts a cyclic prefix (CP)  221  to be transmitted with the data  222 . 
       FIG. 4  shows schematically OFDM symbols in time domain in accordance with the transmission technique applicable to this invention. Time data stream  400  at a particular one of the orthogonal frequencies includes plural time slots. Time slot (Sym T)  410  includes CP  411  and data  412  assembled as taught above in conjunction with  FIGS. 2 and 3 . The next time slot (Sym T+1) 420 includes CP  421  and data  422 . In accordance with the transmission system applicable to this invention, the data of Sym T+1  420  may differ from the data of earlier Sym T  410 , or these symbols include the same data for transmission redundancy.  FIG. 4  illustrates the time domain stream  400  applicable to one of the orthogonal frequencies of the transmission protocol. Other time domain data streams similar to time domain stream  400  are applicable to the other orthogonal frequencies. 
       FIG. 5  schematically illustrates a technique called block spreading described in co-pending U.S. patent application Ser. No. 11/627,035 entitled “METHOD AND APPARATUS FOR INCREASING THE NUMBER OF ORTHOGONAL SIGNALS USING BLOCK SPREADING” filed Jan. 25, 2007, now U.S. Pat. No. 8,005,153 (claiming priority from U.S. Provisional Patent Application No. 60/762,071 filed Jan. 25, 2006) applied to orthogonal frequency division multiplexing access (OFDMA) system.  FIG. 5  illustrates an OFDMA system with block spreading, where user signal [c k ( 0 ) . . . c k (L−1)] is transmitted in N OFDM time slots in time stream  400  with a block spreading code of length N. The block spreading code is denoted as [s m ( 0 ), s m ( 1 ) . . . s m (N−1)] for the user equipment m. Note in the preferred embodiment a different block spreading code is assigned to each user equipment in any one cell  104 ,  105  and  106 . The block spreading codes are orthogonal to each transmitting UE in a cell, therefore, allowing concurrent transmission of multiple UEs at the same time frequency resource without inter-user interference. 
     For each OFDMA time slot user signal [c k ( 0 ) . . . c k (L−1)]  201  is modulated in respective modulation blocks  511 ,  521  . . .  581 . This modulation can be the OFDMA modulation block illustrated in  FIG. 2  or the single-carrier OFDMA modulation block shown in  FIG. 3 . Other OFDM related modulation blocks are possible including but not limited to OFDM, DFT-spread OFDM, single-carrier OFDM and DFT-spread OFDMA. For the nth (for n=1 to N) OFDM time slot where block spreading is applied for the particular UE  109 , the modulated signals are multiplied by a common scale s m (n−1) ( 512 ,  522  . . .  582 ) in respective multipliers  513 ,  523  . . .  583 . The number of transmissions N can be any plural number. This processing results in a time stream  400  including block spreading time slots  430 ,  440  . . .  490 . These N OFDM time slots may be discontinuous in time as shown in  FIG. 5  or they may be sequential and continuous in time. If these N OFDM time slots are discontinuous the time intervals between these time slots are not necessarily equal. 
       FIG. 6  schematically illustrates one embodiment of the block scrambling for OFDMA systems of this invention. The block scrambling code is designated as [g i ( 0 ), g i ( 1 ), . . . g i (N−1)] for cell i. For each OFDMA time slot user signal [c k ( 0 ) . . . c k (L−1)]  201  is modulated in respective modulation blocks  511 ,  521  . . .  581  as previously described. For the nth (for n=1 to N) OFDM time slot where block spreading is applied for the particular UE  109 , the modulated signals are multiplied by a common scale s m (n−1) ( 512 ,  522  . . .  582 ) in respective multipliers  513 ,  523  . . .  583 . For the nth (for n=1 to N) OFDM time slot where block spreading is preferably applied for the particular cell, the modulated signals are multiplied by a common scale g i (n−1) ( 611 ,  621  . . .  681 ) in respective multipliers  612 ,  622  . . .  682 . Transmission of the block-scrambled signals can be contiguous or non-contiguous in time.  FIG. 6  illustrates a non-contiguous, but the block scrambling of this invention can be applied to contiguous OFDM symbols in the time domain. Further, non-contiguous transmissions need not have the same time interval spacing. 
     In a multi-cell OFDMA system, inter-cell interference is typically the dominant factor that influences the system performance such as cell average throughput or cell edge throughput. The block spreading OFDMA system shown in  FIG. 5  provides minimal intra-cell interference by orthogonally separating the signals from a plurality of UEs with UE specific orthogonal block spreading code. The preferred embodiment of this invention employs a similar technique to combat inter-cell interference. Consider the case of two UEs  109  of adjacent cells, each located near the common cell boundary. Since the UEs  109  in this case are in differing cells, they may have the same block spreading code. Without further mechanism for inter-cell interference randomization, the interference UEs  109  observe from each other are largely identical, on the N time slots over which block spreading is applied. Block scrambling in the preferred embodiment of this invention is cell specific. In other words, difference cells assign different block scrambling codes [g i ( 0 ), g i ( 1 ), . . . g i (N−1)] to its serving UEs. Therefore, cell specific block scrambling codes decorrelates signals from these UEs  109  and randomizes inter-cell interference over a plurality of time slots. 
       FIGS. 7 and 8  illustrate alternative embodiments of this invention. Note that g i (n) is a common factor to all samples in one OFDM symbol. Thus, it can be multiplied to the signal before or after the modulation blocks  511 ,  521  . . .  581 . This is illustrated in  FIG. 7  where respective multipliers  612 ,  622  . . .  682  multiply the user signal [c k ( 0 ) . . . c k (L−1)]  201  before modulation blocks  511 ,  521  . . .  581 . Further, the order of applying s m (n) and g i (n) to an OFDM symbol is exchangeable.  FIG. 8  illustrates another alternate embodiment where the multiplication of respective multipliers  612 ,  622  . . .  682  occurs between multiplication in respective multipliers  513 ,  523  . . .  583  and the modulation of respective modulation blocks  511 ,  521  . . .  581 . In fact the modulation and multiplications are commutative and can be performed in any order. 
     In the preferred embodiment the block scrambling code is common to all users in one cell. Substantial advantageous decorrelation results from cell specific block scrambling codes. Each UE  109  can obtain the block scrambling code from its serving cell through the broadcast channel or the control channel. The block scrambling sequence should have a length equal to or greater than the number of repeat time periods. The block scrambling codes can be any sequences, but preferably are constant amplitude sequences where the absolute value of g i (n) is the same (for n=1, 2 . . . N). In particular, a block scrambling sequence may be any pseudo random sequence, e.g. the m-sequence. Other embodiments of block scrambling codes are Hadamard codes, DFT codes and CAZAC sequences. CAZAC sequences are complex valued sequences with following properties: 1) Constant Amplitude (CA); and 2) Zero Cyclic Autocorrelation (ZAC). Examples of CAZAC sequences include but are not limited to: Chu Sequences; Frank-Zadoff Sequences; Zadoff-Chu (ZC) Sequences; and Generalized Chirp-Like (GCL) Sequences. 
     Zadoff-Chu (ZC) sequences are defined by:
 
 a   M ( k )=exp[ j 2π( M/N )[ k ( k+ 1)/2+ qk]] for N odd  
 
 a   M ( k )=exp[ j 2π( M/N )[ k   2 /2+ qk]] for N even  
 
where: N is the length of the sequence; M is the index of the root ZC sequence with M and N being relatively prime; q is any fixed integer; and k is the index of the sequence element ranging from 0 to N−1. These are representative examples of CAZAC sequences. An alternative convention for ZC definition replaces j in the above formula by −j. Either convention can be adopted. In the above formula, making N a prime number maximizes the set of non-orthogonal root ZC sequences having optimal cross-correlation. When N is prime, there are (N−1) possible choices for M. Each such choice results in a distinct root ZC CAZAC sequence. Block scrambling sequence hopping is also possible within a cell or among cells.
 
     The length of the block scrambling code is not necessary the same as the length of the block spreading code. Further, block scrambling can be applied to OFDMA systems without block spreading. In OFDMA systems, block scrambling can be applied to the transmission of any signals such as the reference signal, user data signals, acknowledge signals, channel quality indicator signals and random access preambles. 
     The block scrambling method of this invention can be applied to OFDMA, OFDM, FDMA, DFT-spread OFDM, DFT-spread OFDMA, single-carrier OFDMA (SC-OFDMA), and single-carrier OFDM (SC-OFDM) systems. These versions of FDM transmission strategies are not mutually exclusive, since, for example, single-carrier FDMA (SC-FDMA) may be realized using the DFT-spread OFDM technique. In addition, embodiments of the invention also apply to general single-carrier systems. 
     The block scrambling method of this invention applies to both downlink and uplink transmissions. In a downlink transmission, a common transmitter or base station communicates to multiple UEs at the same time slot, while separating different UEs signal on mutually orthogonal sub-carriers in frequency domain. In downlink transmission, block spreading enables the base station to communicate to plural UEs at the same time frequency resource. In an uplink transmission, a plurality of UEs are communicating to a common receiver or base station in a time slot, on mutually orthogonal sub-carriers in frequency domain. In uplink transmission, block spreading enables a plurality of UEs to communicate to a base station on the same time frequency resource. The block scrambling method of this invention applies to both downlink and uplink transmissions, in additional to or independent of block spreading. 
     The block scrambling code can be receiver specific or transmitter specific. For example, in uplink transmission, each receiver or base station has a specific block scrambling sequence. In downlink transmission, the base station applies a common block scrambling sequence to signal transmission of its serving UEs. Both scenarios result to cell specific block scrambling code per base station. 
       FIG. 9  illustrates method of transmitting signals in a communication system over at least two time periods of this invention. Block  701  generates a base signal including at least two samples in each time period. Block  702  selects a scrambling sequence of length equal to or greater than the number of time periods. Block  703  scales all samples in the signal in a time period with one element of the scrambling sequence and transmitting the scaled signal in the time period. Block  704  modulates the scrambled and scales base signal on a radio frequency carrier. Block  705  transmits the modulated radio frequency carrier.