Upper and lower bounds on the capacity and minimum energy-per-bit for general additive white Gaussian noise (AWGN) and frequency-division AWGN (FD-AWGN) relay channel models are established. First, the max-flow min-cut bound and the generalized block-Markov coding scheme are used to derive upper and lower bounds on capacity. These bounds are never tight for the general AWGN model and are tight only under certain conditions for the FD-AWGN model. Two coding schemes that do not require the relay to decode any part of the message are then investigated. First, it is shown that the "side-information coding scheme" can outperform the block-Markov coding scheme. It is also shown that the achievable rate of the side-information coding scheme can be improved via time sharing. In the second scheme, the relaying functions are restricted to be linear. The problem is reduced to a "single-letter" nonconvex optimization problem for the FD-AWGN model. The paper also establishes a relationship between the minimum energy-per-bit and capacity of the AWGN relay channel. This relationship together with the lower and upper bounds on capacity are used to establish corresponding lower and upper bounds on the minimum energy-per-bit that do not differ by more than a factor of 1.45 for the FD-AWGN relay channel model and 1.7 for the general AWGN model.

The capacity of a class of discrete-memoryless relay channels with orthogonal channels from the sender to the relay receiver and from the sender and relay to the receiver is shown to be equal to the max-flow min-cut upper bound. The result is extended to additive white Gaussian noise (AWGN) relay channels where the channel from the sender to the relay uses a different frequency band from the channel from the sender and the relay to the receiver.

This paper describes the capacity of frequency-division AWGN relay channels with linear relaying functions. A sequence of nonconvex optimization problems solving are also described in this paper

The paper develops algorithms for minimizing the energy required to transmit packets in a wireless environment. It is motivated by the following observation: In many channel coding schemes it is possible to significantly lower the transmission energy by transmitting packets over a long period of time. Based on this observation, we show that for a variety of scenarios the offline energy-efficient transmission scheduling problem reduces to a convex optimization problem. Unlike for the special case of a single transmitter-receiver pair studied by (see Prabhakar, Uysal-Biyikoglu and El Gamal. Proc. IEEE Infocom 2001), the problem does not, in general, admit a closed-form solution when there are multiple users. By exploiting the special structure of the problem, however, we are able to devise energy-efficient transmission schedules. For the downlink channel, with a single transmitter and multiple receivers, we devise an iterative algorithm, called MoveRight, that yields the optimal offline schedule. The MoveRight algorithm also optimally solves the downlink problem with additional constraints imposed by packet deadlines and finite transmit buffers. For the uplink (or multiaccess) problem MoveRight optimally determines the offline time-sharing schedule. A very efficient online algorithm, called MoveRightExpress, that uses a surprisingly small look-ahead buffer is proposed and is shown to perform competitively with the optimal offline schedule in terms of energy efficiency and delay.

In this paper, we investigate the use of M-ary infrared CDMA technique in wireless infrared networks. It is shown that this method is highly capable in providing the multiple access facility for downlinks of infrared wireless networks. The results show that the M-ary CDMA technique, which fully utilizes the properties of optical orthogonal codes, achieves better BER performance in comparison with ordinary infrared CDMA networks. The main advantages are the reduction in bandwidth, power, and the elimination of threshold-setting at the receiver.

We compare various receiver structures for optical CDMA networks. Optical orthogonal codes (OOC) are utilized as signature sequences and the performance studied in this paper takes into account the effect of all major noise sources. The required mean number of photon count per chip time for reliable transmission of data bits for various receiver structures is investigated. Two general classes of receivers are investigated which use chip-time or bit-time electronic integration. The results show that receivers with chip-time integration have superior performance and therefore low-power transmission is possible at low speeds. However, the high-speed systems need bit-time integration and therefore should operate at higher levels of signal power.

Indoors wireless infrared transmission is severely impaired by ambient noise. In addition, in a multiple user network, since many users share the same physical channel, considerable amount of multi-user interference will also be introduced. Infrared CDMA techniques are proposed to combat the effect of ambient and multi-user interference. Our analysis is based on photon counting approach and the bit error rate is given versus signal power. The results show that using infrared CDMA techniques, transmission can be performed well below the ambient noise power with transmission power that satisfies eye-safety power regulations.