Abstract-This paper considers the suitability of a range of multi-input-multi-output (MIMO) orthogonal frequency-division multiplexing architectures for use in urban hotspots. A ray-tracing propagation model is used to produce realistic MIMO channel data. This information is used to determine the expected throughput and area coverage for various physical (PHY) layer schemes. Site-specific throughput predictions are generated in a city-center environment. Link adaptation (LA) is shown to play a key role in the choice of space-time algorithm, the use of adaptive modulation and coding, and the number of antennas employed at both ends of the radio link. No single PHY layer scheme is suitable to cover the entire coverage area. Results demonstrate the need for MIMO LA under a wide range of channel conditions. For the area under test, 2% of covered locations selected a spatial multiplexing (SM) scheme, 50% selected a space-time block coding (STBC) scheme, and 48% selected a hybrid SM/STBC scheme. With suitable power control and LA, for the scenario under consideration, high peak capacities and good geographic coverage were achieved.Index Terms-Link adaptation (LA), orthogonal frequencydivision multiplexing (OFDM), power control, propagation, space-time block codes (STBCs), spatial multiplexing (SM).

Abstract-The latest mobile WiMAX standard promises to deliver high data rates over extensive areas and to large user densities. More specifically, data rates are expected to exceed those of conventional cellular technologies. The IEEE 802.16e Wi-MAX standard enables the deployment of metropolitan area networks to mobile terminals in non-line-of-sight radio environments. Current concerns include leveraging high data rates, increasing area coverage, and competing with beyond 3G networks. Based on the IEEE 802.16e wirelessMAN-OFDMA (Orthogonal Frequency Division Multiple Access) physical (PHY) layer air-interface, this paper presents a physical layer study of MIMO enabled mobile WiMAX in an urban environment. The radio channels are based on those developed in the European Union IST-WINNER project. Results are given in terms of system throughput and outage probability with and without relays for a range of SISO, MISO and MIMO architectures. Results show that satisfactory performance cannot be achieved in macrocells unless radio relays are used in combination with MIMO-STBC.

Abstract-This paper presents a set of rigorous and comprehensive coverage and throughput studies for enhanced high-capacity Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems. A ray-tracing propagation model has been used to produce site-specific MIMO channel data. Site-specific throughputs are then predicted in a city centre environment for a range of different physical layer configurations. Dynamic Transmit Power Control (TPC) is applied to lower transmit power and thus reduce interference. Results demonstrate the need for suitable link adaptation strategies under a wide range of channel conditions. Spatial Multiplexing (SM) is shown to struggle in regions close to the basestation, or for locations with low SNR. We conclude that it is vital to reconfigure parameters on a case by case basis. When a suitable space-time algorithm is combined with Adaptive Modulation and Coding (AMC) and the appropriate number of antenna elements, high peak throughputs and good geographic coverage become realistic for wireless applications in a dense urban environment.

Abstmcl-Investigating advanced signal processing algorithms for existing and future wireless systems, this paper has mainly focussed on evaluating the potential performance improvements that accrue from cancelling the common pilot channel's interference in terms of hit error rate performance for downlink applications. The impact of different cancellation strategiessequential (SIC) and parallel (PIC) -has been presented for various data rates and channel profiles. With the investigative analysis appertaining to the FDD element of the UTRAN specified by 3GPP, the performance of the interference cancellation unit is primarily based on the elimination of the cross-correlation of the spreading codes over time dispersive wireless conditions. With a sound channel estimate, the results are shown to achieve near interference free performance highlighting the potentiality of these interference cancellation schemes. Their versatility and robustness against channel estimation errors is further demonstrated by a relative performance comparison for a diversified range of data rates, pilot-to-data power ratios and channel conditions.

Abstract-WiMAX (802.16e) is technically capable of offering city-wide broadband connections to a high number of mobile terminals. The technology has strong industrial support, however a number of challenges remain to be resolved. Major concerns include battery life for mobile terminals, balancing support for high velocity and high data-rate, and increasing area coverage. Relay technology is a promising approach to address these challenges. Due to limited radio resources, it is necessary to consider radio resource efficiency. This paper presents a de-tailed analysis of relay efficiency with and without resource sharing. To enhance spectral efficiency, a directional distributed relaying architecture is proposed for interference elimination and avoidance.