Wireless ATM (W-ATM) networks have been studied extensively. The extension of ATM network services to the wireless environment faces many interesting problems. The original ATM network was designed for high-speed noiseless, reliable channels. None of these characteristics are applicable to the wireless channel. One of the most critical aspects of a W-ATM network is the medium access control (MAC) protocol used by mobile terminals (MTs) to request service from the base station (BS), which has to consider the quality of service (QoS) of the specific application. In this article the authors analyze some MAC protocols, particularly those for TDMA systems, and discuss their advantages and disadvantages.

The physical layer of an orthogonal frequency division multiplexing (OFDM) wireless communication system, operating in full-duplex (FD) mode is implemented in this paper, using GNU Radio software and universal software radio peripheral (USRP) hardware technology. The self-interference cancellation (SIC) is achieved on the FD node by applying four different techniques, two in the radio frequency (RF) domain and two in the digital domain. In the RF domain, a passive suppression is obtained by placing the transmit (Tx) and the receive (Rx) antennas such that they generate orthogonal electromagnetic fields. Also, an active signal suppression is achieved by changing the phase and attenuating the self-interference (SI) Tx signal, to generate a local SIC signal. The SIC signal and the Rx signal are then combined before going to the low noise amplifier at the FD node. In the digital domain, two techniques are applied to improve the interference cancellation and the quality of the link: firstly, virtual differentiation of the Tx and Rx signals is achieved by using OFDM symbols with different sizes; secondly, a spreading and precoding technique utilizing the discrete Fourier transform (DFT) is considered. In order to test the practical operation of the FD node, two simultaneous links between the three nodes are established. The results of the implemented system show that the SI can be reduced up to 58 dB which, along with the two digital techniques, allows to have two simultaneous links with a bit error rate similar to the one achieved with just one link without interference, increasing the spectral efficiency.

A method for reducing feedback in a downlink multiuser MIMO-OFDM cellular system, with zero forcing beamforming at the base (BS) and antenna combining at each mobile (MS) is proposed. The method consists of partitioning the subcarriers into groups, choosing the quantized channel vector that better represents each group in terms of average quantization error. Numerical results show that savings up to 93% in overhead bits are obtained for SNR equal to 15 dB, with reductions in channel capacity that goes from 30% to 50% depending on the codebook size used for quantization.

This letter proposes three methods to jointly calculate beamforming and combining vectors for the downlink of TDD multiuser multiple-input multiple-output systems. The algorithms use quantized information of the beamformers to get the corresponding combiners, maximizing the signal-to-interference-plus-noise-ratio. Two of the proposed methods exceed in performance those already published. The third method reduces the feedforward overhead with a light degradation in performance. Our three proposals are based on a perfect interference cancellation at the transmitter before calculating the quantized beamformers.

Full-duplex (FD) is a very promising technique that offers the potential to double the spectral efficiency. In this paper, the achievable rate for uplink-downlink user and antenna selection in poor scattering channels of FD multiuser system is studied. The considered FD communication system consists of one FD multi-antenna base station (BS) and multiple half duplex (HD) single antenna mobile terminals (MTs). Simulation results show the achievable sum-rate for practical number of users in the system.