Ephraim Zehavi

A pragmatic approach to trellis-coded modulation

Since the early 1970s, for power-limited applications, the convolutional code constraint length K=7 and rate 1/2, optimum in the sense of maximum free distance and minimum number of bit errors caused by remerging paths at the free distance, has become the de facto standard for coded digital communication. This was reinforced when punctured versions of this code became the standard for rate 3/4 and 7/8 codes for moderately bandlimited channels. Methods are described for using the same K=7, rate 1/2 convolutional code with signal phase constellations of 8-PSK and 160PSK and quadrature amplitude constellations of 16-QASK, 64-QASK, and 256-QASK to achieve, respectively, 2 and 3, and 2, 4, and 6 b/s/Hz bandwidth efficiencies while providing power efficiency that in most cases is virtually equivalent to that of the best Ungerboeck codes for constraint length 7 or 64 states. This pragmatic approach to all coding applications permits the use of a single basic coder and decoder to achieve respectable coding (power) gains for bandwidth efficiencies from 1 b/s/Hz to 6 b/s/Hz.<<ETX>>

Performance of power-controlled wideband terrestrial digital communication

Performance of a wideband multipath-fading terrestrial digital coded communication system is treated. The analysis has applications to a cellular system using direct-sequence spread-spectrum code-division multiaccess (CDMA) with M-ary orthogonal modulation on the many-to-one reverse (user-to-base station) link. For these links, power control of each multiple-access user by the cell base station is a critically important feature. This feature is implemented by measuring the power received at the base station for each user and sending a command to either raise or lower reverse link transmitter power by a fixed amount. Assuming perfect interleaving, the effect of the power control accuracy on the system performance is assessed. >

On the performance evaluation of trellis codes

Generating function techniques for analyzing the error event and the bit-error probabilities for trellis codes are considered. The conventional state diagram approach for linear codes where the number of states is equal to the number of trellis states cannot be applied directly to arbitrary trellis codes, and instead, a state diagram where the number of states is equal to the square of the number of trellis states must be used. It is shown that for an interesting class of trellis codes a modified generating function can be defined for which the number of states {em is equal to} the number of trellis states. The class of codes considered includes trellis codes of rate R=(n-1)/n based upon set partitioning whenever the first partition breaks the signal constellation into two subsets which have the same configuration matrix, i.e., the same ordered set of mutual distances. The complexity of calculating this modified generating function is the same as for the ordinary generating function of a convolutional code with the same number of trellis states. Bounds on the performance of some interesting codes are given based upon this method.

Cooperative Game Theory and the Gaussian Interference Channel

In this paper we discuss the use of cooperative game theory for analyzing interference channels. We extend our previous work, to games with N players as well as frequency selective channels and joint TDM/FDM strategies. We show that the Nash bargaining solution can be computed using convex optimization techniques. We also show that the same results are applicable to interference channels where only statistical knowledge of the channel is available. Moreover, for the special case of two player 2 times K frequency selective channel (with K frequency bins) we provide an O(K log2 K) complexity algorithm for computing the Nash bargaining solution under mask constraint and using joint FDM/TDM strategies. Simulation results are also provided.

Multichannel Opportunistic Carrier Sensing for Stable Channel Access Control in Cognitive Radio Systems

In this paper we propose to use the well known game theoretic Gale-Shapley stable marriage theorem from game theory as a basis for spectrum allocation in cognitive radio networks. We analyze the performance of the proposed solution and provide tight lower and upper bounds on both the stable allocation and the optimal allocation performance. Then we present a novel opportunistic multichannel medium access control technique that achieves stable allocation within a single CSMA contention window. We discuss practical implementation issues and put forward two other varieties of the algorithm which have lower implementation complexity. Finally, we provide simulated examples.

Game theory and the frequency selective interference channel

As discussed in this paper, the frequency selective interference channel is important, both from a practical as from an information theoretic point of view. We show that it has many intriguing aspects from a game theoretic point of view as well, and that various levels of interference admit different types of game theoretic techniques.

Bargaining Over the Interference Channel

In this paper we analyze the interference channel as a conflict situation. This viewpoint implies that certain points in the rate region are unreasonable to one of the players. Therefore these points cannot be considered achievable based on game theoretic considerations. We then propose to use Nash bargaining solution as a tool that provides preferred points on the boundary of the game theoretic rate region. We provide analysis for the 2times2 interference channel using the FDM achievable rate region. We also outline how to generalize our results to other achievable rate regions for the interference channel as well as the multiple access channel

Performance analysis of a multilevel coded modulation system

A modified version of the multilevel coded modulation scheme of Imai and Hirakawa (1977) is presented and analyzed. In the transmitter, the outputs of the component codes are bit interleaved prior to mapping into 8-PSK channel signals. A multistage receiver is considered, in which the output amplitudes of the Gaussian channel are soft limited before entering the second and third stage decoders. Upper bounds and Gaussian approximations for the bit error probability of every component code, which take into account errors in previously decoded stages, are presented. Aided by a comprehensive computer simulation, it is demonstrated in a specific example that the addition of the interleaver and soft limiter in the third stage improves its performance by 1.1 dB at a bit error probability of 10/sup /spl minus/5/, and that the multilevel scheme improves on an Ungerboecks code with the same decoding complexity. The rate selection of the component codes is also considered and a simple selection rule, based on information theoretic arguments, is provided. >

P/sup 2/ codes: pragmatic trellis codes utilizing punctured convolutional codes

A single convolutional code of fixed rate can be punctured to form a class of higher rate convolutional codes. The authors extend this pragmatic approach to the case where the core of the trellis decoder is a Viterbi decoder for a punctured version of the de facto standard, rate 1/2 convolutional code. >

Stable matching for channel access control in cognitive radio systems

In this paper we propose a game theoretic approach to the allocation of channels to multiple cognitive users who share a set of frequencies. The famous Gale-Shapley stable matching algorithm is utilized to compute the channel allocations. We analyze the stable matching performance for the case of cognitive resource allocation and prove that in contrast to the general case, in the cognitive resource allocation problem there is a unique stable matching. We then show that the stable matching has performance very close to the optimal centralized allocation. It always achieves at least half of the total rate of the centralized allocation and under Rayleigh fading it achieves about 96% of the total centralized rate. Comparisons to random channel allocations are also discussed.