Rate-compatible punctured convolutional codes (RCPC codes) andtheir applications

The concept of punctured convolutional codes is extended by punctuating a low-rate 1/N code periodically with period P to obtain a family of codes with rate P/(P+l), where l can be varied between 1 and (N-1)P. A rate-compatibility restriction on the puncturing tables ensures that all code bits of high rate codes are used by the lower-rate codes. This allows transmission of incremental redundancy in ARQ/FEC (automatic repeat request/forward error correction) schemes and continuous rate variation to change from low to high error protection within a data frame. Families of RCPC codes with rates between 8/9 and 1/4 are given for memories M from 3 to 6 (8 to 64 trellis states) together with the relevant distance spectra. These codes are almost as good as the best known general convolutional codes of the respective rates. It is shown that the same Viterbi decoder can be used for all RCPC codes of the same M. the application of RCPC codes to hybrid ARQ/FEC schemes is discussed for Gaussian and Rayleigh fading channels using channel-state information to optimise throughput     

On linear structure and phase rotation invariant properties ofblock M-PSK modulation codes

Two important structural properties of block M(=2^' )-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S_M-PSK=(0,1,2,---,M-1) under modulo-M addition. Then the linear structure of block M-PSK modulation codes over S_M-PSK with respect to modulo- M vector addition is defined, and conditions are derived under which a block M-PSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block M-PSK modulation code that is linear as a binary code to be invariant under 2^h/180°M phase rotation, for 1⩽h⩽l is derived. Finally, a list of short 8-PSK and 16-PSK modulation codes is given, together with their linear structure and the smallest phase rotation for which a code is invariant     

Rotationally invariant trellis-coded modulations withmultidimensional M-PSK

Using a multidimensional approach, the author discovers a large family of rotationally invariant trellis-coded M-PSK (M-ary shift keying) schemes, M⩾8, with nominal coding gains ranging from 3 to 5 dB and with bandwidth requirements the same as, or even less than, those of uncoded M/2-PSK schemes at the same information bit rate. The rotationally invariant schemes have performance and complexities comparable to the best known nonrotationally-invariant trellis-coded two-dimensional M-PSK schemes. Computer simulation results for these schemes, assuming an additive white-Gaussian-noise (AWGN) channel, are reported     

A concatenated coded modulation scheme for error control

A concatenated coded modulation scheme is presented for error control in data communications. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary phase-shift keying (PSK) modulation. Error performance of the scheme is analyzed for an additive white Gaussian noise (AWGN) channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner-code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The scheme is particularly effective for high-speed satellite communications for large file transfer where high reliability is required. A simple method is also presented for constructing block codes for M-ary PSK modulation. Soome short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45° rotation     

A simple derivation of the power spectrum of full-response CPM andsome of its properties

Using a new representation for continuous-phase modulated (CPM) signals, it is shown how a closed-form expression for the power spectral density of full-response M-ary CPM with modulation index J /M can be obtained by straightforward computations. This result is used to provide an explanation of the fact that this power spectral density depends only on J and not on M     

Fully digital M-ary PSK and M-ary QAMdemodulators for land mobile satellite communications

A fully digital implementation of digital modems is the preferred option of system designers because high performance can be achieved at reasonable cost. The author explains the beneficial features inherent in fully digital demodulator implementations. Other features which are required for land mobile satellite communication systems are also discussed. Recently reported techniques for the synchronisation and detection of M-ary PSK and M-ary QAM modulation schemes are reviewed with emphasis placed on those which are well suited to digital implementation     

Semi-analytical performance evaluation in satellite digital linksin the presence of interference

A model for the semi-analytic performance evaluation of digital satellite radio links in the presence of interference on both the uplink and the downlink is presented. Error probability on the linear portion of the link is estimated using simulation to determine the moments of the interfering signal samples and analyzing the effect of an undetermined phase difference among carriers. The nonlinear portion of the link is modeled using a series expansion of the nonlinearity; the output terms are then separated, allowing construction of the conditional probability densities required in the error probability computation. Results are carried out for M-QAM (M-ary quadrature amplitude modulation) and M-PSK (M-ary phase-shift keying) modulation systems     

Frequency-hopped multiple access communications with coding andside information

The authors consider frequency-hopped spread-spectrum multiple-access communications using M-ary modulation and error-correction coding. The major concerns are multiple-access interference and the network capacity in terms of the number of users that can transmit simultaneously for a given level of codeword error probability. Block coding is studied in detail. The authors first consider the use of Q-ary Reed-Solomon (RS) codes in combination with M-ary modulation with mismatched alphabets so that Q>M. It is shown that the network capacity is drastically reduced in comparison with the system with matched alphabets. As a remedy, the use of matched M-ary BCH codes is proposed as an alternative to mismatched RS codes. It is shown that when the number of users in the system is large, a BCH code outperforms an RS code with a comparable code rate and decoding complexity. The authors consider the use of a robust technique for generation of reliable side information based on a radio-threshold test. They analyze its performance in conjunction with MFSK and error-erasure correction decoding. It is shown that this nonideal ratio-threshold method can increase the network capacity in comparison with the system with perfect side information     

Design of coded CPFSK modulation systems for bandwidth and energyefficiency

Consideration is given to the problems related to the design of M-ary continuous-phase frequency-shift keying (CPFSK) systems with modulation index h=J/M, combined with eternal rate r binary convolution encoders. The following questions are raised and answered: (1) how should different encoder-modulator systems be compared and how can comparable systems be recognized from the system parameters, i.e. M, h, and r?; (2) what are the limits on the information rate per unit bandwidth, versus signal-to-noise ratio, when reliable transmission is required?; (3) how does one choose the system parameters M, h, and r when the overall system has to achieve a specified performance?; and (4) how does one design the external rate r binary convolutional encoder to put in front of the M-ary CPFSK modulation system with h=J/M ? A simple approximation for the bandwidth of a CPFSK signal is given and shown to be sufficiently accurate for system design purposes. The design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder-modulator system and thus yields improved performance for a given demodulation-decoding complexity compared to previous approaches for the design of coded CPFSK systems     

Limiter-discriminator detection of a coherent optical heterodyneM-ary CPFSK receiver

The performance of a coherent optical M-ary continuous-phase frequency-shift-keying (CPFSK) receiver using limiter-discriminator (L-D) detection is investigated. It is shown that L-D detection of CPFSK optical signals offers the best performance for a large normalized IF beat spectral linewidth, ΔνT. When the modulation index is unity, the receiver is immune to laser phase noise and can produce (M/4) exp (-SNR) symbol error probability, which may be considered as the upper bound if the optimal modulation index is used (SNR is the signal-to-noise ratio per symbol). Optimum modulation indexes are 0.8 and 1 at ΔνT=1% and ΔνT=2%, respectively, for M=4, 8, and 16     

An ARQ scheme using combined QPSK and BPSK transmissions

We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented     

A differentially coherent receiver for minimum shift keying signal

The author extends to the case of minimum-shift-keying (MSK) modulation the differentially coherent reception theory established for phase-shift-keying modulation. A novel differentially coherent detector for MSK is thus derived. The receiver filter is equivalent to the cascade of a matched filter and an equalizer in order to suppress inherent intersymbol interference. It is shown that performance can be improved when the delay between signals, multiplied by the differential detector, is increased from one to M bit time intervals. This decreases the effect of noise correlation and, thus, the bit error probability. The bit error probability of the proposed receiver is calculated. It is found that almost all potential improvement due to the delay M is obtained with M=3     

Performance analysis of RS-coded M-ary FSK forfrequency-hopping spread spectrum mobile radios

Decoding performance of Reed-Solomon (RS) coded M-ary FSK with noncoherent detection in a frequency-hopping spread spectrum mobile radio channel is theoretically analyzed. Exact formulas and an approximate one for evaluating word error rates (WERs) of error correction and error-and-erasure correction schemes on decoding the RS codes are derived. It is shown that with K symbol erasure and C symbol error detection, RS coded M-ary FSK achieves the equivalent diversity order of (K+1)(C+1)     

Asymptotic results for partial concentrators

Various switching network construction advantageously use modules known as partial concentrators. A partial concentrator is an n-input, m-output, single-stage switching device in which each input has access to some but not all of the outputs. A partial concentrator is said to have capacity c, if, for any k⩽c inputs, there exist k disjoint paths from the k inputs to some set of k outputs. Here, capacity values achievable for large n when each input has access to exactly M outputs, are considered. For a partial concentrator in which each input has access to exactly M outputs, it is shown that the cost ratio can be made arbitrarily small for any fixed M⩾2. In addition, it is shown that the rate of decrease of the cost ratio with increasing n is logarithmic for M=2, and polynomial for M⩾3     

A selective ARQ protocol with a finite-length buffer

Of the automatic-repeat-request (ARQ) techniques commonly used in communication systems, selective protocols, while the most efficient, have the notable drawback of requiring large buffers at the receiver side. A selective ARQ protocol with a finite-length buffer is described. If N is the number of codewords transmittable in the round-trip delay, the protocol requires a buffer length N+N_a , N_a⩾2 being an integer. A lower bound on the throughput of the protocol is derived. It achieves higher throughputs than similar schemes giving results comparable to those for selective protocols with infinite-length buffer for high error rates in the communication channel     

Spectral shaping and digital synthesis of an M-ary timeseries

The use of pulse shaping to control transmitted spectral density precisely is examined. A digital filter architecture is described that not only mitigates the traditional problems of lengthy development intervals and cost manufacturing methods, but offers the additional features of intrinsically coding high-speed binary (M=2) data into M-ary symbols while ensuring highly reproducible, baud-normalized, transmitter pulse shaping. A conceptual basis for the digital synthesis method is first described, including a functional circuit appropriate to the simplest filter realizations. Spectral effects internal to the filter are considered, and a simple method to obtain desired transmitted spectra is outlined. It is shown that even relatively short pulses used in high-level modulation systems lead to impractical memory storage demands; however, the simple expedient of segmenting the finite impulse function greatly reduced the individual memory requirements, though it necessitates intermediate adding operations. Experimental examples illustrate the design methodology for quaternary (M=4) data signals in a Nyquist communication channel and serve as points of reference for addressing performance and design flexibility     

On the symbol error probability of maximum-selection diversityreception schemes over a Rayleigh fading channel

The symbol error probability of two selection schemes, namely, maximum signal-to-noise ratio (Mγ) selection and maximum output (MO) selection, for M-ary multidiversity reception over a Rayleigh fading channel are discussed. The symbol error probability of the MO scheme is lower than that of the Mγ scheme. The more diversity receptions that are used, the larger is the difference. A simple expression of crossover average signal-to-noise ratio (per bit) is presented as a guideline for increasing the number of diversity receptions     

M-architecture: a structural model of traffic managementand control in broadband ISDNs

A model of multiservice network architecture (M-architecture) is presented. An attempt is made to describe the traffic management and control schemes in a systematic way. The basic concepts are developed, and examples are given that indicate how the proposed framework can be used to solve multiplexing, routing, and flow control problems in the ISDN. The emphasis is on the traffic control schemes. The M-architecture can be regarded as either a reference architecture for future multiservice networks or an abstract model of traffic management and control in currently used networks     

Optimisation of parameters in an MFSK transmission system

An optimisation technique for maximising the information throughput of an M-ary frequency-shift keyed (MFSK) transmission system is described. An upper bound for the error-free throughput of the system in the presence of additive white Gaussian noise (AWGN) for different numbers of tones, M, is derived. From this, the optimum range for M can be identified