We formulate antenna impedance estimation in a classical estimation framework under correlated Raleigh fading channels. Based on training sequences of multiple packets, we derive the ML estimators for antenna impedance and channel variance, treating the fading path gains as nuisance parameters. These ML estimators can be found via scalar optimization. We explore the efficiency of these estimators against Cramer-Rao lower bounds by numerical examples. The impact of channel correlation on impedance estimation accuracy is investigated.

Mutual coupling among receive antennas can profoundly reduce capacity in multiple-input, multiple-output (MIMO) systems. Prior work has shown that these losses can often be significantly reduced by using sophisticated antenna matching at the receiver. However, previous studies have focused exclusively on frequency non-selective matching, and rely on assumptions that are valid only for small bandwidths. In this paper, we consider the capacity of broadband MIMO-OFDM systems with coupled receive antennas. We present upper and lower bounds on the best capacity that can be achieved by physically realizable, frequency-selective antenna matching. The upper and lower bounds coincide for most antenna configurations considered in the examples, and thus determine the performance of capacity-optimal matching. These results suggest that frequency-selective matching can significantly increase capacity in the presence of strong coupling. Moreover, these gains can be achieved by a simple class of matching networks that are easily realized in hardware.

Mutual coupling among receive antennas can profoundly reduce the ergodic capacity of MIMO systems. Prior work has shown that these losses can often be mitigated by using multi-port antenna matching at the receiver; however, previous studies have focused exclusively on frequency-nonselective matching and rely on assumptions which are valid only for small bandwidths. In this paper, we revisit the ergodic capacity of a MIMO system with coupled receive antennas for a non-negligible bandwidth. In particular, we present upper and lower bounds on the best possible MIMO capacity that can be achieved by physically-realizable, frequency-selective (FS) multi-port and single-port matching networks. These results suggest that FS matching can significantly increase capacity in the presence of strong coupling, for both single-port and multi-port scenarios. Moreover, we show that these gains can be achieved for a 2 × 2 MIMO system by a simple class of matching networks that are easily realized in hardware.

In order to support multiple antennas on compact wireless devices, transceivers are often designed with matching networks that compensate for mutual coupling. Some works have suggested that when optimal matching is applied to such a system, performance at the center frequency can be improved at the expense of an apparent reduction in the system bandwidth. This paper addresses the question of how coupling impacts bandwidth in the context of circular arrays. It will be shown that mutual coupling creates eigen-modes (virtual antennas) with diverse frequency responses, using the standard matching techniques. We shall also demonstrate how common communications techniques such as Diversity-OFDM would need to be optimized in order to compensate for these effects.

We undertake an information-theoretic approach to characterize the optimal design of a broadband multi-antenna system in the presence of mutual coupling. It was shown recently that mutual coupling effectively decomposes otherwise spectrally-identical spatial modes of an antenna array into spectrally non-identical eigen-modes. We shall use Shannon's information theory and Fano's broadband matching theory to develop optimal transceiver designs for a compact broadband MIMO system. It will be shown that in the presence of channel state information, optimal transmit power allocation and matching characteristic follow a mutual space-frequency water-pouring solution.

Traditional antenna selection applied to MIMO systems ignores the presence of unselected (or inactive) antennas. However, compact arrays offer a unique advantage in that mutual coupling can be exploited to improve the system performance. Previous studies on selection with coupling have not considered the effects of the inactive-antenna terminations and lack detailed transceiver modeling. In this work, we present a communication-theoretic analysis and design of antenna selection systems for compact transceivers. We also propose a simple parasitic antenna selection technique that can significantly outperform traditional selection when coupling is present.

The number of unmanned vehicles and devices deployed underwater is increasing. New communication systems and networking protocols are required to handle this growth. Underwater free-space optical communication is poised to augment acoustic communication underwater, especially for short-range, mobile, multi-user environments in future underwater systems. Existing systems are typically point-to-point links with strict pointing and tracking requirements. In this paper we demonstrate compact smart transmitters and receivers for underwater free-space optical communications. The receivers have segmented wide field of view and are capable of estimating angle of arrival of signals. The transmitters are highly directional with individually addressable LEDs for electronic switched beamsteering, and are capable of estimating water quality from its backscattered light collected by its co-located receiver. Together they form enabling technologies for non-traditional networking schemes in swarms of unmanned vehicles underwater.

The front-end is a crucial component in modern wireless communication systems. For SISO systems minimizing the front-end noise factor is optimal, and this also applies to MIMO systems with i.i.d. noise. However, for compact MIMO receivers that may exhibit spatially correlated noise, e.g., through antenna mutual coupling, the optimal design procedure is not clear. In this paper we develop MIMO low-noise design principles from a communication theory perspective by deriving generalizations of SNR and noise factor from various MIMO communication schemes. As one result, we are able to derive optimal matching networks for a bank of uncoupled amplifiers.

Practical wireless devices are considered too small to support multi-antenna communications. Several studies have proposed optimal MIMO transceiver design in the presence of mutual coupling by use of matching networks. However, most studies assume a narrowband model. For broadband systems, Fano's matching theory reveals gain-bandwidth trade-offs for physically realizable networks. In this paper, we formulate matching network design for broadband coupled multi-antenna transceivers with circular arrays and investigate the role coupling plays in determining the RF bandwidth of the system. It will be shown that in the presence of coupling, the spatial modes of an antenna array have different bandwidths and that for 2-element arrays with practical bandwidths, a quarter-wavelength spacing is good enough.

We present an information theoretic perspective on optimal broadband matching. Most of the broadband matching and communication theory literature assumes a frequency-flat reflection coefficient. We derive the optimal capacity and matching network characteristic for a broadband system from an information theoretic view point while incorporating the broadband matching limitations. We also propose an iterative algorithm to arrive at the optimal solution. We illustrate by an example that a white characteristic for a matching network is often sub- optimal for a system with a non-white transfer function.

The impact of antenna mutual coupling on signal correlation in multi-antenna receivers has been studied in great detail. By contrast, there has been little work on how mutual coupling affects noise. In this paper we present a noise model for a diversity receiver that includes noise generated by the antennas, front-end amplifiers, and other receiver components. This model shows that noise in a compact diversity receiver may be spatially correlated. Expressions relating noise correlation to properties of the antennas and amplifiers are derived and its impact on the outage probability of an optimal diversity combiner is studied. Examples illustrating the relationship between mutual coupling and noise correlation demonstrate how different noise sources may impact performance in profoundly different ways.

The diversity-multiplexing tradeoff for multiple-input multiple-output (MIMO) point-to-point channels and multiple access channels were first proposed and studied by Zheng and Tse recently. While the optimal tradeoff curves for MIMO channels have been explicitly explored, those corresponding to some suboptimal and practical MIMO schemes are still open. One such important problem is the diversity-multiplexing tradeoff for a V-BLAST type system employing ordered successive interference cancellation (SIC) receivers with zero forcing (ZF) or minimum mean square error (MMSE) processing at each stage. In this paper, we take a novel geometrical approach and rigorously verify that under general settings, the optimal ordering rule for a V-BLAST SIC receiver will not improve its performance regarding diversity-multiplexing tradeoff in point-to- point channels. The same geometrical tool is then applied to MIMO spatial-division multiple access channels, leading to some first results in this area. Particularly, we reveal that when the rates of data streams are fixed (i.e., zero spatial multiplexing gain), the diversity order is not improved by user ordering.

The effect of antenna mutual coupling on fading correlation in compact MIMO arrays has received considerable attention. By contrast, relatively little attention has been paid to the noise. In this paper we present a circuit model for a noisy MIMO receiver front-end that includes arbitrary coupling and noise correlation. The noise figure for two-port networks is extended to multiport networks, from which theorems for optimal front-end design are derived. Numerical results are presented which provide insight into receiver noise behavior in the presence of coupled antennas.

We consider the impact of transmitter correlation, mutual coupling and matching networks on the design and performance of MIMO MRC systems with limited feedback. We present codebook design techniques for three measures of transmitted power and we investigate the impact of antenna matching on the performance of these codebooks. Numerical results suggest that, regardless of the power measure and matching networks, the benefits of MIMO MRC with limited feedback can be achieved with antennas spaced as close as 0.2 - 0.3 wavelengths apart.

In this paper, we provide a theoretical, simulation and experimental characterization of the performance of linear arrays of tri-polarized dipole antennas in multiple input multiple output (MIMO) systems in terms of degrees of freedom and channel capacity. Specifically, we formulate three distinct approaches, theoretical and experimental, that lead to the conclusion that linear arrays of tri-polarized dipole antennas employed at the transmit and receive end of a MIMO system can achieve a three-fold increase in channel capacity with respect to analogous arrays of linearly polarized antennas.

Previous studies of receive diversity have carefully modeled the impact of spatial correlation and antenna coupling on the signal component at the receiver. By contrast, relatively little attention has been paid to noise. In this paper we introduce a receive diversity model that articulates the dominant physical noise sources and relates their spatial correlation to the properties of the antennas, front-end amplifiers and matching networks. We then derive an optimal receiver as well as a formula for the resulting outage probability in terms of these noise sources. Numerical results are presented which suggest that different noise sources can impact performance in profoundly different ways.

We consider the impact of transmitter correlation and mutual coupling on MIMO MRC systems. We present optimal transmission strategies for three input power metrics as well as formulas for the resulting outage probabilities. Numerical results suggest that, regardless of the power metric, most of the performance benefits of MIMO MRC can be obtained with transmit antennas spaced as close as 0.2 - 0.3 wavelengths.

The diversity-multiplexing tradeoff for MIMO point-to-point channels and multiple access channels are first proposed and studied in [4][5]. While the optimal tradeoff curves for MIMO channels have been explicitly explored, those corresponding to some practical MIMO schemes are still open. One such example, as mentioned in [4][5], is the diversity-multiplexing tradeoff problem for ordered successive interference cancellation (SIC) receivers, which is the focus of this paper. In literature, the impact of the optimal ordering on the diversity order for V-BLAST SIC receivers is analyzed for 2-layer scenarios [2][3][6], but only conjectured for larger number of layers through numerical results [2][7]. In this paper, based on a novel geometrical analysis, we prove that under general settings, any ordering rule for a V-BLAST SIC receiver will not improve its performance regarding diversity-multiplexing tradeoff. Furthermore, extending the study to multiple access channels, we show that the two extreme points of the tradeoff curve remain unchanged regardless of ordering, which motivates us to predict that the whole tradeoff curve is the same as that of fixed-order detectors.

In recent years, the remarkable ability of multiple-input-multiple-output (MIMO) wireless communication systems to provide spatial diversity or multiplexing gains has been clearly demonstrated. For MIMO diversity schemes, it is well known that antenna selection methods that optimize the postprocessing signal-to-noise ratio (SNR) can preserve the diversity order of the original full-size MIMO system. On the other hand, the diversity order achieved by antenna selection in spatial multiplexing systems, especially those exploiting practical coding and decoding schemes, has not thus far been rigorously analyzed. In this paper, a geometrical framework is proposed to theoretically analyze the diversity order achieved by transmit antenna selection for separately encoded spatial multiplexing systems with linear and decision-feedback receivers. When two antennas are selected from the transmitter, the exact achievable diversity order is rigorously derived, which previously only appears as conjectures based on numerical results in the literature. If more than two antennas are selected, we give lower and upper bounds on the achievable diversity order. Furthermore, the same geometrical approach is used to evaluate the diversity-multiplexing tradeoff in spatial multiplexing systems with transmit antenna selection

We propose a new unitary matrix code for differential space-time modulation that is useful for two transmit antennas and a large number of receive antennas. We optimize the design of this code with respect to the Euclidean distance criterion. To reduce decoding complexity, we derive two suboptimal low-complexity receivers that allow individual data symbols in the code to be sequentially decoded. Simulation results show that the new codes outperform some existing codes, and that the low-complexity receivers approach the performance of maximum-likelihood decoding in the high-rate, large-array regime.

In the context of antenna selection for MIMO diversity systems, the problem of optimal diversity order is well addressed. On the other hand, the diversity order achieved by antenna selection in spatial multiplexing systems, especially those exploiting practical coding and decoding schemes, has not been rigorously analyzed thus far. In Zhang, H, et al. (2005), we propose a new geometrical framework for theoretically analyzing the achievable diversity order when L = 2 transmit antennas are selected for an N/sub R/ /spl times/ N/sub T/ SM system with linear receivers. In this paper, we extend it to the general scenarios with 2 /spl les/ L /spl les/ N/sub T/, and both linear and decision feedback receivers are considered. A diversity order of (N/sub T/-L+1)(N/sub R/-L+1) are rigorously shown to be achievable by the optimal selection, which was previously partly conjectured by other researchers through simulation results.

We consider the asymptotic behavior of the capacity of multiple-antenna Rayleigh-fading channels in the limit as the transmit and receive arrays become large. We show that the capacity converges in distribution to a Gaussian random variable, and give closed-form formulas for its mean and variance. These results enable us to derive the first asymptotic formula for outage rates, as well as a sharper estimate of the error in previously reported asymptotic formulas for ergodic capacity. Although these formulas are asymptotic, we show by simulation that they are often quite accurate, even for relatively small arrays.

Most wireless communication systems currently employ single- or dual-polarized antennas which measure one or two components of the received electromagnetic (EM) signal. In this paper, we investigate the performance gains achievable by using "vector antennas" that can detect or excite up to six independent degrees of freedom.

Bit-interleaved space-time coded modulation (BI-STC), which combines serial concatenation of bit-interleaved coded modulation (BICM) with space-time block codes, can effectively exploit the available diversity in space and time under various fading conditions. In this letter, we propose to use iterative decoding to further improve the performance of BI-STC by exploiting the concatenating structure of the codes. The decoding metric is therefore modified to fit for the iterative process, and the derived error bounds suggest that set-partition labeling instead of gray labeling should be used when considering iterative decoding.

We consider a direct-sequence multihop packet radio network using slotted ALOHA in a Rayleigh fading environment. We are interested in optimally choosing the transmission range, code rate, and slotted ALOHA transmission probability to be used by each node. We use a new performance measure, information efficiency, to analyze the network and show that the information efficiency of the low-cost mobile packet radio network can be improved approximately 20 fold by using the optimum parameters. We suggest a practical trellis-coded modulation scheme which comes close to realizing the theoretic limits found.

The paper considers joint channel estimation and data sequence detection for multipath radio channels with multiple antennas at the transmitter and/or receiver. An iterative space-time receiver based on the expectation-maximization algorithm is proposed. We examine the performance of this receiver for transmit diversity and space-time coding methods over Rayleigh fading channels. Simulation results show that the receiver can often achieve near-coherent performance with modest complexity and using very few pilot symbols.

Most analytical studies of the performance of space diversity systems on fading channels assume a very rich multipath environment. In certain wireless applications, however, the number of significant multipath components can be small. In this letter, we consider a multipath channel in which the signal propagates from the transmitter to the receiver via L discrete paths which are uniformly distributed about the transmitter and receiver. For this channel, we study the effects of the number of multipath components and antenna array size on the error probability and outage capacity of space diversity systems. We observe that performance is significantly influenced by the presence of a channel with few multipath components.

We consider the design of space-time constellations based on group codes for fading channels with multiple transmit and receive antennas. These codes can be viewed as multiantenna extensions of phase-shift keying (PSK), in the sense that all codewords have equal energy, all are rotations of a fixed codeword, and there is a simple differential transmission rule that allows data to be sent without channel estimates at the transmitter or receiver. For coherent detection, we show that all optimal full-rank space-time group codes are unitary (each code matrix has equal-energy, orthogonal rows). This leads to a simpler code design criterion and suggests that unitary codes may play an important role in coherent as well as noncoherent communication. For any number of transmit antennas t, we then use the design criterion to characterize all full-rank unitary space-time group codes of minimum block length (also t) which have 2/sup p/ codewords. These results allow us to characterize all optimal 2/sup p/-ary unitary group codes with square code matrices. This restricted class of block codes matches the class proposed for differential modulation by Hughes (see IEEE Trans. Inform. Theory, vol.46, p.2567-78, Nov. 2000), and by Hochwald and Sweldens (see IEEE Trans. Commun., vol.48, p.2041-2052, Dec. 2000).

A bit-interleaved space-time coded OFDM system is considered in this paper for frequency-selective fading channels. As OFDM divides a frequency-selective fading channel into a set of parallel flat fading channels, space-time block codes for flat fading are transmitted from each subcarrier by multiple transmit antennas to guarantee space diversity, and code bits are bit-wise interleaved across the subcarriers before being grouped and mapped to space-time block code to obtain frequency diversity. Performance bounds and simulation results show that the bit-interleaved space-time coded OFDM system can effectively exploit both space and frequency diversity to improve performance.

We consider a general, synchronous, randomly-spread code-division multiple-access transmission scheme in which the transmitted data is any linear combination of the data and the spreading sequences are not tied to any specific transmit antenna. For large user populations, we characterize the spectral efficiency (capacity per chip) as a function of the array size, signal-to-noise ratio and the number of users per chip in the presence of frequency flat fading.

An adaptive receiver based on per-survivor processing is proposed for detecting space-time trellis codes transmitted over time-selective flat-fading channels, and its performance is examined through simulations. Results suggest that the new receiver can outperform iterative approaches based on Kalman filtering and the expectation-maximization algorithm, at the cost of increased receiver complexity.

We consider the design of robust codes that exploit both space and time diversity, using bit-interleaved coded modulation. Under quasi-static fading conditions, codes constructed in this way achieve full diversity and perform close to the best space-time trellis codes of comparable complexity. Under fast-fading conditions, these same codes achieve higher diversity than previously known codes of the same complexity.

We consider the impact of transmit diversity on the capacity of synchronous, randomly-spread code-division multiple-access, in the presence of frequency-flat fading. For large user populations, we characterize the spectral efficiency (capacity per chip) of two systems that use different spreading sequences on each antenna: a theoretically optimal system in which each transmit antenna is fed by independent data streams, and a code sequence diversity scheme that transmits the same data on each antenna.

Most existing space-time coding schemes assume time-invariant fading channels and offer antenna diversity gains relying on accurate channel estimates at the receiver. Other single differential space-time block coding schemes forego channel estimation but are less effective in rapidly fading environments. Based on a diagonal unitary matrix group, a novel double differential space-time block coding approach is derived in this paper for time-selective fading channels. Without estimating the channels at the receiver, information symbols are recovered with antenna diversity gains regardless of frequency offsets. The resulting transceiver has very low complexity and is applicable to an arbitrary number of transmit and receive antennas. Approximately optimal space-time codes are also designed to minimize bit error rate. System performance is evaluated both analytically and with simulations.

This paper considers joint channel estimation and data detection for multipath radio channels with multiple antennas at the transmitter and/or receiver. An iterative space-time receiver based on the expectation maximization (EM) algorithm is described and performance is investigated on fast fading channels for several transmit diversity and space-time coding schemes.

Most existing space-time coding schemes assume time-invariant fading channels and offer antenna diversity gains relying on accurate channel estimates at the receiver. Based on a diagonal unitary matrix group, a novel double differential space-time block coding approach is derived for time-selective fading channels. Without estimating the channels at the receiver, information symbols are recovered with antenna diversity gains regardless of the frequency offsets. The resulting transceiver has very low complexity and is applicable to an arbitrary number of transmit and receive antennas. Approximately optimal space-time codes are also designed to minimize the bit error rate. System performance is evaluated both analytically and with simulations.

We consider a frequency-hopping multihop packet radio network using M-ary frequency-shift keying modulation in a Rayleigh fading environment. Each node transmits packets using an extended (n, k) Reed-Solomon code and the slotted ALOHA channel access protocol. For this network, we determine the optimum transmission range, optimum code rate, and optimum slotted ALOHA transmission probability to be used by each node in the network. Tradeoffs in choosing the transmission range and code rate, and the spectral efficiency of the network are captured in a new performance measure, information efficiency, which is analogous to expected forward progress. Maximizing the information efficiency yields the optimum desired network parameters.

Space-time coding and modulation exploit the presence of multiple transmit antennas to improve the performance on multipath radio channels. Thus far, most work on space-time coding has assumed that perfect channel estimates are available at the receiver. In certain situations, however, it may be difficult or costly to estimate the channel accurately, in which case it is natural to consider the design of modulation techniques that do not require channel estimates at the transmitter or receiver. We propose a general approach to differential modulation for multiple transmit antennas based on group codes. This approach ran be applied to any number of transmit and receive antennas, and any signal constellation. We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to construct optimal differential modulation schemes for two transmit antennas. These schemes can be demodulated with or without channel estimates. This permits the receiver to exploit channel estimates when they are available. The performance degrades by approximately 3 dB when estimates are not available.

We consider the design of space-time modulation techniques that do not require channel estimates at the transmitter or receiver. We propose a general approach to differential modulation for multiple transmit antennas based on group codes. This approach can be applied to any number of transmit antennas and any signal constellation. We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to design optimal modulators for two transmit antennas.

We consider a communication channel corrupted by thermal noise and by an unknown and arbitrary interference of bounded energy. For this channel, we derive a simple upper bound to the worst-case error probability suffered by a direct sequence (DS) communication system with error-correction coding, pseudorandom interleaving, and a correlation receiver. This bound is exponentially tight as the block length of the error correcting code becomes large. Numerical examples are given that illustrate the dependence of the bound on the choice of error correcting code, the type of interleaving used, and the relative energy of the Gaussian noise and arbitrary interference.

A fully connected radio network is considered in which packets are sent using slow frequency-hop (FH) modulation, slotted ALOHA random access, and Reed-Solomon (RS) error-control coding. For this network, the dependence of throughput, delay, and drift on the code rate and block length is examined. It is shown that the drift approaches a simple limiting form as the block length becomes large. This form suggests that, in a bistable FH network, the undesirable stable point can usually be eliminated without increasing the delay or reducing the throughput at the desirable stable point. In particular, bistability can be eliminated by increasing the code block length and retransmission delay, and does not require the use of decentralized control or channel traffic estimates.

The capacity of the discrete memoryless arbitrarily varying channel (AVC) is investigated for deterministic list codes with fixed list size L. For every AVC with positive random code capacity C/sub r/, a nonnegative integer M called the symmetrizability is defined. For the average probability of error criterion, it is shown that the list capacity is given by C(L)=C/sub r/ for L>M and C(L)=0 otherwise. Bounds are given which relate C/sub r/ and M. Also, explicit formulas for C(L) are given for a family of noiseless, additive AVCs.

Random access to a packet broadcast channel with large propagation delay is investigated. A protocol is presented that combines slotted ALOHA random access with the use of forward-error-correction (FEC) across transmitted packets. Expressions for the throughput, delay, and drift of this protocol are derived. Numerical studies and asymptotic analyses of the drift indicate that the protocol has a maximum throughput of e/sup -1/ and exhibits bistability and saturation behavior similar to that of slotted ALOHA with immediate feedback. However, unlike ALOHA, bistability and saturation in the code protocol can be eliminated with the proper choice of protocol parameters without increasing the packet delay. It is further shown that, when compared to slotted ALOHA, the code protocol typically achieves a higher throughput and lower delay at system equilibrium with no loss in maximum throughput.

Communication over a waveform channel corrupted by additive white Gaussian noise and by an unknown and arbitrary interference of bounded power is considered. For this channel, an upper bound is presented for the worst-case error probability of a communication system comprising a direct-sequence spread spectrum modulator and a nonlinear correlation receiver. It is shown that this bound is exponentially tight as the number of chips used in the modulator becomes large. This bound is evaluated for several detector nonlinearities. Numerical examples and comparisons to the performance of a pure Gaussian noise channel are also given.

Coding schemes for the T-user binary adder channel are investigated. Recursive constructions are given for two families of mixed-rate, multiuser codes. It is shown that these basic codes can be combined by time-sharing to yield codes approaching most rates in the T-user capacity region. In particular, the best codes constructed herein achieve a sum-rate, R/sub 1/+...+R/sub T/, which is higher than all previously reported codes for almost every T and is within 0.547-bit-per-channel use of the information-theoretic limit. Extensions to a T-user, Q-frequency adder channel are also discussed.

The minimum probability of error achievable by random codes on the arbitrarily varying channel (AVC) is investigated. New exponential error bounds are found and applied to the AVC with and without input and state constraints. Also considered is a simple subclass of random codes, called randomly modulated codes, in which encoding and decoding operations are separate from code randomization. A universal coding theorem is proved which shows the existence of randomly modulated codes that achieve the same error bounds as "fully" random codes for all AVCs.

The minimum average error probability achievable by block codes on the two-user multiple-access channel is investigated. A new exponential upper bound is found which can be achieved universally for all discrete memoryless multiple-access channels with given input and output alphabets. It is shown that the exponent of this bound is greater than or equal to those of previously known bounds. Moreover, examples are given where the new exponent is strictly larger.

The random-code capacity region of a multiple-access arbitrarily varying channel subject to both state and input constraints is determined. Consideration of a simple erasure channel shows that the capacity region is not convex in general.>

It is well known that orthogonal signal sets approach the channel capacity and reliability function of the infinite bandwidth additive white Gaussian noise channel. It is shown that pseudonoise-modulated orthogonal signals play a similar role for the infinite bandwidth Gaussian arbitrarily varying channel.>

Communication over a waveform channel corrupted by additive white Gaussian noise, and by an unknown and arbitrary interfering signal of bounded power is considered. For this channel, the authors derive an upper bound to the worst case error probability of direct-sequence spread spectrum communication with a correlation receiver, and also a lower bound applicable to any binary signaling technique and any receiver. By comparing these two bounds, it is shown that, if a small error probability is required, then no other binary signaling scheme or receiver can substantially improve upon the performance of direct-sequence with a correlation receiver for the same power and bandwidth.>

A new upper bound to the probability of error in detecting one of M equally probable signals in additive white Gaussian noise is presented. This bound is easy to calculate, can be applied to any signal set. It is always better than the union and minimum distance bounds. Examples demonstrate the use of the bound.>

The arbitrarily varying channel (AVC) models a channel with unknown parameters that change with time in an arbitrary way from one symbol transmission to the next. The relationship between the error probability suffered on the AVC by a deterministic code with random block interleaving and the error probability predicted by an unknown, fixed channel model (i.e. a compound channel) is investigated. The main results are that codes of this form can achieve the same error exponents as fully random codes. Optimal codes (those achieving the exponent) can be designed by choosing codes appropriate for the associated compound channel.>

The main objective is to develop exponential bounds to the best error probability achievable with random coding on the Gaussian arbitrarily varying channel (GAVC) in the one case where a (strong) capacity exists (i.e., with peak time-averaged power constraints on both the transmitter and interference). The GAVC models a channel corrupted by thermal noise and by an unknown interfering signal of bounded power. The upper and lower bounds to the best error probability achievable on this channel with random coding are presented. The asymptotic exponents of these bounds agree in a range of rates near capacity. The exponents are universally larger than the corresponding exponents for the discrete-time Gaussian channel with the same capacity. It is further shown that the decoder can be taken to be the minimum Euclidean distance rule at all rates less than capacity.>

Coherent communication over a waveform channel corrupted by thermal noise and by an unknown and arbitrary interfering signal of bounded power is considered. For a fixed encoder, a random modulator/demodulator (modem) and detector are derived. They asymptotically minimize the worst-case error probability as the blocklength of the encoder becomes large. This optimal modem is independent of the encoder, and the optimal detector is the standard correlation receiver. A simple upper bound to the performance of any encoder when used with the optimal modem and detector is presented. These results provide a benchmark with which the performance of spread-spectrum modems and robust detection rules can be compared.>

The random coding capacity of a vector Gaussian arbitrarily varying channel (VGAVC) is determined, along with a simple general method for computing this capacity. The VGAVC is a discrete-time memoryless vector channel with an input power constraint and additive Gaussian noise that is further corrupted by an additive jamming signal. The statistics of this jamming signal are unknown and can be arbitrary, subject only to a power constraint.>

The {\em arbitrarily varying channel} (AVC) can be interpreted as a model of a channel jammed by an intelligent and unpredictable adversary. We investigate the asymptotic reliability of optimal random block codes on Gaussian arbitrarily varying channels (GAVC's). A GAVC is a discrete-time memoryless Gaussian channel with input power constraintP_{T}and noise powerN_{e}, which is further corrupted by an additive "jamming signal." The statistics of this signal are unknown and may be arbitrary, except that they are subject to a power constraintP_{J}. We distinguish between two types of power constraints: {\em peak} and {\em average.} For peak constraints on the input power and the jamming power we show that the GAVC has a random coding capacity. For the remaining cases in which either the transmitter or the jammer or both are subject to average power constraints, no capacities exist and only\lambda-capacities are found. The asymptotic error probability suffered by optimal random codes in these cases is determined. Our results suggest that if the jammer is subject only to an average power constraint, reliable communication is impossible at any positive code rate.