Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
  • H04L27/22—Demodulator circuits; Receiver circuits
  • H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
  • H04L27/2271—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses only the demodulated signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
  • H04L27/22—Demodulator circuits; Receiver circuits
  • H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
  • H04L27/2275—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses the received modulated signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
  • H04L27/22—Demodulator circuits; Receiver circuits
  • H04L27/233—Demodulator circuits; Receiver circuits using non-coherent demodulation
  • H04L27/2332—Demodulator circuits; Receiver circuits using non-coherent demodulation using a non-coherent carrier
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
  • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
  • H04L27/38—Demodulator circuits; Receiver circuits
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0058—Allocation criteria
  • H04L5/006—Quality of the received signal, e.g. BER, SNR, water filling
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
  • H04L2025/03375—Passband transmission
  • H04L2025/03401—PSK
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/03592—Adaptation methods
  • H04L2025/03598—Algorithms
  • H04L2025/03611—Iterative algorithms
  • H04L2025/03649—Algorithms using recursive least square [RLS]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying

Definitions

• the present invention relates to communication systems.
• the present invention relates to estimation of carrier phase and amplitude in a receiver in a communication system using a phase shift keying modulation scheme.
• the transmitted signal typically undergoes time offset (delay), phase shift and attenuation (amplitude change). These effects must be compensated for at the receiver, and the performance of the receiver can depend greatly on the accuracy of the estimates of these parameters.
• time offset has been previously handled and we focus on the problem of estimating the phase shift and attenuation of the signal at the receiver.
• signalling constellations that have symbols evenly distributed on the complex unit circle, such as, binary phase shift keying (BPSK), quaternary phase shift keying (QPSK) and M -ary phase Shift keying ( M - PSK).
• BPSK binary phase shift keying
• QPSK quaternary phase shift keying
• M -PSK M -ary phase Shift keying
• L is the total number of symbols transmitted.
• the block may be an arbitrary number of symbols selected by the receiver or the size of the block may be determined based upon a communication system parameter such as a predetermined frame size.
• pilot symbol a symbol which is known to the receiver and data symbols as symbols which are unknown to the receiver.
• data symbols which are known can be treated as pilot symbols in the discussion that follows.
• the symbol is encoded based upon the change in phase in successive symbols, and thus, unlike the coherent case, the receiver does not need to estimate the carrier phase.
• a popular approach to multiple symbol differential detection is the so called non-data aided, sometimes also called non-decision directed, estimator based on the paper of Viterbi and Viterbi (A. Viterbi and A. Viterbi, " Nonlinear estimation of PSK-modulated carrier phase with application to burst digital transmission," IEEE Trans. Inform. Theory, vol. 29, no. 4, pp. 543 - 551, Jul. 1983).
• the idea is to ' strip' the modulation from the received signal by taking y t l to the power of M .
• a method for estimating the carrier phase and amplitude in a received signal comprising a plurality of symbols modulated using one or more M-ary phase shift keying digital modulation schemes, the plurality of symbols comprising a plurality of pilot symbols known to the receiver, and a plurality of data symbols unknown to the receiver, the method comprising:
• the plurality of symbols may be a block of symbols.
• the optimum value need not be a global optimum, and may simply be an optimum for the set of candidate estimates obtained.
• the sorted order is an ascending order of the M-ary rounded phase offsets.
• the objective function is a sum of squares function.
• the sum of squares function is minimised with respect to estimation of the carrier phase and amplitude.
• the number of modulation schemes is
• and H 0(L)
• the sum of squares value is a weighted sum of squares value.
• the weighting is based upon a Signal to Noise Ratio (SNR) to give more importance to pilot symbols when the SNR is low.
• SNR Signal to Noise Ratio
• the step of determining an optimum candidate val ue from the plurality of candidate values is performed as plurality of candidate values are calculated.
• each candidate value is calculated it is compared with a current optimum candidate value, and if the calculated candidate value is optimal compared to the current optimum candidate value, the current optimum candidate value is updated with the calculated candidate value.
• the current optimum candidate value is updated, a corresponding carrier phase and an amplitude value is calculated.
• the plurality of symbols are modulated using a single M-ary phase shift keying digital modulation scheme. In one aspect, the method implements the algorithm presented in Table 1 below. [0018] In a further aspect, the plurality of symbols are modulated using two or more A/-ary phase shift keying digital modulation schemes. In one aspect, the method implements the algorithm presented in Table 2 below.
• a non-transitory processor readable medium comprising instructions for causing a processor to implement the method of the first aspect.
• a receiver comprising: a receiver module for receiving a signal
• a processing module comprising a memory and a processor operatively coupled to the memory and configured to implement the method of the first aspect.
• a communication system comprising a transmitter and a receiver according to the third aspect, wherein the transmitter implements one or more -ary phase shift keying digi tal modulation schemes and transmits a plurality of symbols comprising a plurality of pilot symbols known to the receiver, and a plurality of data symbols unknown to the receiver.
• MSE Mean Square Error
• MSE Mean Square Error
• MSE Mean Square Error
• Figure 6 is a flowchart of an embodiment of a method for estimating the carrier phase and amplitude in a received signal according to an embodiment
• Figure 7 is a block diagram of a receiver according to an embodiment.
• Embodiments of a method for estimating the carrier phase and amplitude in a received signal comprising a plurality of Symbols modulated (or encoded) using one or more M-ary phase shift keying digital modulation schemes will now be described.
• the method considers the case where the plurality of transmitted symbols comprises both a plurality of pilot symbols known to the receiver and a plurality of data symbols unknown to the receiver.
• the method may be stored on a processor readable medium and implemented by a receiver in a communication system.
• Embodiments of the method use an efficient algorithm for optimised estimation (such as least-squares estimation) of the carrier phase and ampli tude which exploits knowledge of pilot symbols (indexed by P ) in addition to the unknown data portion of the received signal (indexed by D ).
• Optimising techniques define an objective function which is then optimised (eg typically maximised or minimised) to obtain (or select) an estimate or value that represents an optimal solution.
• optimised eg typically maximised or minimised
• sub-optimal solutions may be selected whether there is some advantage such as reduced execution time (eg if the sub-optimal solution is typically within a threshold of the optimal solution at some confidence level).
• One optimisation technique is least squares estimation. In the present case, we can define a sum of squares objective function:
• SS( ⁇ d t ,i e D ⁇ ) can be computed in 0(L) arithmetic operations.
• Y candidate sum value
• Q the candidate sum of squares value and observe that obtaining Q allows determining the full sum of squares term SS in (9) as L and A are constants. That is, the candidate sum value and candidate sum of squares value will refer to calculated values of in (8) and SS in (9) respectively, or suitable variations of those quantities which allow determination of those quantities (such as Q ).
• the candidate sum of squares value may be obtained from calculating the full term or some other term from which the full term can be calculated such as Q , or even some term that is correlated with the full term eg the term is proportional or functionally related to the full term to serve as a suitable proxy calculation for SS .
• the largest candidate square sum value Q will be the sum of squares value that minimises the sum of squares SS .
• the notation L I is often used to denote rounding to the nearest integer and to distinguish this case the subscript 2 ⁇ / ⁇ has been added. That is, if the rounding function L I takes i ts argument to the nearest integer then,
• ⁇ ,( ⁇ ) does not depend on the amplitude p .
• u t ⁇ ff is not strictly inside the set ⁇ ⁇ ⁇ , 2 r( ⁇ ' ) ⁇ , but this is not of consequence, as we intend its value to be considered equivalent modulo 2 ⁇ .
• (16) be a function mapping the interval [0,2 ⁇ ") to a sequence of M -PSK symbols indexed by the elements of D . Observe that f &) is piecewise continuous. The subintervals of [0, 2 ⁇ ) over which f ⁇ &) remains constant are determined by the values of ⁇ z i e D) .
• each candidate sum value Y k can be computed from its predecessor Y k _ ⁇ in a constant number of operations, and given Y k , the value of SS(f k ) can be computed in a constant number of W
• the sort function requires sorting
• the Sort function is the primary bottleneck in this algorithm when L is large. The loops on lines 1 and 11 and the operations: on lines 6 to 9 all require 0(L) or less operations.
• An algorithm for calculating a least squares estimator of the carrier phase and amplitude with pilot and data symbols according to an embodiment.
• the soi function in step 10 may be performed using standard (efficient) sorting algorithms such as found in numerical libraries.
• the sort function returns the sorted indices of the phase offsets (ie the positions of the symbols in D, or equivalently L), or otherwise allows the sorted indices to be determined.
• the sort could sort the values, from which the indices could be obtained.
• the sorting performed in step 10 could be performed as part of (ie integrated into) the loop of the data symbols in steps 1-5 so that the sorted order of -ary rounded phase offsets is obtained upon completion of the loop.
• the order of this value within the set of i-J previously calculated values could be determined and stored.
• a data structure such as an array, linked list, hierarchical tree, etc could be used to store the sorted indexes and once the i' H value is obtained, the index i of the data symbol could be inserted into the appropriate location in this data structure.
• a stopping or early loop termination condition is added to loop steps 1 1 to 17 to save looping through the entire set of H - M ⁇ D ⁇ candidate mapping sequences.
• a possible stopping criterion is if the candidate sum of squares value exceeds a predetermined threshold value. Whilst this may be a suboptimal value it may be sufficiently close for the estimation purposes and may further reduce the number of operations required.
• a threshold value could be obtained from simulations or other data, such as data from experimental trials or operational data. Further, in some embodiments, the exact terms calculated could be varied.
• the value Q that is calculated is not actually the full sum of squares term (ie SS in (9)) but rather a value (or term) from which the full term may be calculated.
• Q represents the varying or non-constant component of the full sum of squares term ( SS in (9)) from which the full term can be calculated (for a given set of pilot symbols and total number of symbols L ).
• the candidate sum of squares value calculated in steps 8 and 14 could be the full term SS rather Q .
• ⁇ 5000 replications are performed to obtain T estimates p , . ..,p T and ⁇ ⁇ , . .., ⁇ ⁇ .
• , L , illustrated using filled circles ( ⁇ ) 42 and cross (x) 41 symbols respectively (for each value of L, subscripts a, b, c).
• the figure depicts an interesting phenomenon.
• L 2048 and
• 256 .
• G be the set of integers for which D m is not empty, ie > 0 if, and only if , tn e G is the number of data symbols modulated according to the m" 1 modulation scheme).
• the rounding in equations ( 11 )( 13)( 12) is performed by rounding to the nearest multiple of 2/r/m where m is the modulation scheme for the symbol being rounded (ie the -ary rounded phase offsets are each rounded with respect to corresponding modulation scheme for the symbol the phase offset is being calculated for).
• m the modulation scheme for the symbol being rounded
• the -ary rounded phase offsets are each rounded with respect to corresponding modulation scheme for the symbol the phase offset is being calculated for.
• O(L) .
• ⁇ , ..., 1 ⁇ be an enumeration of the triples from T sorted in ascending order of the first element in the triple, that is, if t k — ⁇ t kl ,t k2 ,t k ⁇ ) then t a ⁇ t kl whenever i ⁇ k .
• Table 1 The algorithm in Table 1 is modified as outlined in Table 2 below.
• An algorithm for calculating a least squares estimator of the carrier phase and amplitude with pilot and data symbols for multiple -ary phase shift keying digital modulation schemes is an algorithm for calculating a least squares estimator of the carrier phase and amplitude with pilot and data symbols for multiple -ary phase shift keying digital modulation schemes.
• FIG. 22 Return a Return least squares estimate of complex amplitude
• MSE mean square error
• Embodiments of a method for estimating the carrier phase and amplitude in a received signal, comprising a plurality of symbols modulated (or encoded), using one or more -ary phase shift keying digital modulation schemes have been discussed.
• the method considers the case where the plurality of transmitted symbols comprises both a plurality of pilot symbols known to the receiver and a plurality of data symbols unknown to the receiver.
• Figure 6 illustrates a flow chart 600 of a method for estimating the carrier phase and amplitude in a received signal comprising a plurality of symbols modulated (or encoded) using one or more -ary phase shift keying digital modulation schemes according to an embodiment.
• the method comprises the steps of:
• Embodiments of the above method provide an improved algorithm for optimal estimation (using a least squares estimator) of the carrier phase and amplitude which exploits knowledge of pilot symbols (indexed by P ) in addition to the unknown data portion of the received signal (indexed by D ).
• the method may be implemented using the algorithms shown in Table I or 2,
• the M-ary rounded phase offset calculated in step 602 are calculated according to the appropriate modulation scheme for the symbol.
• Embodiments of the method utilise recursion to calculate (or computer) candidate estimates and only require O(LlogL) arithmetic operations, where L is the number of received symbols and is thus an efficient estimation method.
• the plurality of candidate values of an objective function calculated in step 606 above correspond with a plurality of candidate estimates of the carrier phase and amplitude.
• calculating the candidate value of the objective function, and selecting an optimum value allows a corresponding optimum estimates of the carrier phase and amplitude to be obtained (ie calculated or determined).
• the determining step 608 is perfbmied as the plurality of candidate values are calculated in step 606.
• corresponding candidate estimates (or values) of the carrier phase and amplitude are calculated (or determined) and stored.
• each of the plurality of candidate estimates is calculated it is compared with current optimum candidate value, if the candidate value is an improvement, (ie more optimal) than the current optimal value, then the previous best values for the candidate value is replaced and the carrier phase and amplitude are calculated and stored as (best) estimates.
• the determining step 608 is performed after the calculation step 606.
• the plurality of candidate values are stored in a matrix, vector, tree, hash, or other data structure. The optimum value could then be obtained from the full set of candidate values, and he corresponding carrier phase and ampl itude for this optimum value could then be determined.
• the corresponding carrier phase and amplitude for each of the plurality of candidate estimates could also be calculated and stored when they are calculated, and once the optimum candidate value is selected, the corresponding carrier phase and amplitude could be determined by looking up the corresponding stored values.
• the objective function may be a sum of squares function, eg (9), and the candidate sum of squares value may be obtained from calculating the full term or some other term from which the full term can be calculated such as Q (the non-constant or varying component in the full term), or even some term that is correlated with the full term, eg the term is proportional or functionally related to the full term to serve as a suitable proxy calculation.
• the optimum may be the minimum sum of squares value.
• a carrier phase and amplitude can be calculated for each candidate value and these can be associated in a memory with the candidate value. For example, in Table 1 , as each improved optimum value of Q is obtained, the associated carrier phase and amplitude is also calculated (or estimated).
• a stopping criterion may be used in which case the plurality of candidate values need not be the full set of possible candidate values ( H in the multi-modulation scheme case).
• the optimum value need not be a global optimum.
• the optimum- value may simply be a good or acceptable value based on some threshold or criteria, such as an indication of convergence such as decreasing change between current and previous optimum values (ie further calculations are only likely to increase the precision and not the accuracy of the estimate of the optimum value).
• a receiver and an associated communication system which implement embodiments of the method described herein can also be provided.
• the communication system may be a wired or wireless communication system.
• Figure 7 is a block diagram 700 of a receiver which implements the above described algorithm.
• the receiver comprises a receiver module 710 and a processing module 720.
• the receiver module comprises a signal receiving module 702 such as input port in a wired implementation or an antenna in a wireless implementation.
• the receiver module 710 receives a transmitted signal and prepares the signal for signal processing tasks performed by the (baseband) processing module.
• the receiver module 710 (the RF front end in the case of RF wireless communications) comprises modules for performing tasks such as filtering and low noise amplification 712, down-conversion to baseband frequencies 714, automatic gain control (AGC) 71.6 and quantisation (eg using an Analog to Digital Converter or ADC) of the received signal 718 to produce a base band signal.
• the (baseband) processing module 720 receives the base band signal and performs a range of signal processing tasks to generate estimates of the transmitted bit stream.
• the baseband processing can be implemented in application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, etc and comprises modules for performing time offset (delay) estimation 722, carrier phase and amplitude estimation 724, demodulation 726, and symbol decoding 728.
• ASICs application specific integrated circuits
• DSPs digital signal processors
• DSPDs digital signal processing devices
• PLDs programmable logic devices
• FPGAs field programmable gate arrays
• the carrier phase and amplitude estimation module is configured to implement embodiments of the method described herein, such as the algorithms shown in Table 1 and Table 2.
• the method is stored as instructions in a non-transitory processor readable medium (eg hard disk, Flash memory, optical disk (CDROM, DVD), etc) for causing a processor to implement the method.
• a non-transitory processor readable medium eg hard disk, Flash memory, optical disk (CDROM, DVD), etc.
• the methods and receivers may be utilised in communication systems and components such as those described in the following co-pending PCT applications:
• processing may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
• ASICs application specific integrated circuits
• DSPs digital signal processors
• DSPDs digital signal processing devices
• PLDs programmable logic devices
• FPGAs field programmable gate arrays
• processors controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
• a central processing unit may be used, containing an Input/Output Interface, an Arithmetic and Logic Unit (ALU) and a Control Unit and Program Counter element which is in communication with input and output devices or modules through the Input/Output Interface, and a memory.
• Software modules also known as computer programs, Computer codes, or instructions, may contain a number a number of source code or object code segments or instructions, and may reside in any computer or processor readable medium such as a RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disk, a removable disk, a CD-ROM, a DVD-ROM or any other form of computer readable medium.
• the computer readable medium may be integral to the processor.
• the processor and the computer readable medium may reside in an ASIC or related device.
• the software codes may be stored in a memory unit and executed by a processor.
• the memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

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