Orthogonal frequency division multiplex (OFDM) has become one of the most popular air-link technologies for future broadband wireless communications. To further improve its bandwidth efficiency and system performance, adaptive resource allocation and smart antenna techniques have been widely used in the OFDM system. However, the use of fully adaptive beamforming in an OFDM system significantly increases the complexity of the medium access control layer design and thus affects the implementation of adaptive resource allocation. A novel cross-layer adaptive resource allocation strategy with hybrid adaptive array and switched-beam smart antennas suitable for the OFDM systems has been proposed. With the help of different smart antennas schemes based on different users' quality of service requirements, the strategy effectively reduces the complexity of adaptive resource allocation in an OFDM system, while still maintaining a satisfactory system performance.

It has been shown that CSI at the transmitter can significantly improve the performance and reliability of multiple antenna multi-user systems. In MIMO OFDM systems the control overhead and signal processing complexity lead to the definition of time-frequency chunks. For all carriers and at all times in the chunk, the same spatial signal processing is applied. In this paper, we study the optimal signal processing using chunks in multi-user MIMO OFDM systems with respect to sum capacity optimization. At first, the optimal single-user chunk capacity optimization is studied and different optimal and suboptimal approaches are proposed. Then, the extension to the spectral power allocation is analyzed. Finally, the multi-user case is addressed. The results are illustrated by numerical simulations based on the IEEE 802.11n channel model

In this paper, a novel MIMO detection named decision feedback aided detection based on lattice reduction (DFDLR) is proposed. Lattice reduction has been proposed to be exploited in signal detection in multiple antenna systems. However, lattice reduction transforms the QAM constellation cube to be a parallelotope, and it is difficult to determine the transformed QAM boundaries, which results in sub-optimal performance with simple quantization. We propose to exploit decision feedback to enhance the QAM boundary control. Simulations show that decision feedback can improve the performance of lattice reduction-based linear detection (LD) and lattice reduction-based successive interference cancellation (SIC) significantly especially with zero forcing (ZF) criterion. It is also shown by simulation that the proposed scheme in conjunction with SIC can approach maximum likelihood (ML) detection with MMSE criterion at high signal-to-noise ratio (SNR)

In this paper, an efficient digital implementation of multicarrier transmission scheme based on generalized discrete Fourier transform (DFT) filter banks is presented for multicarrier code-division multiple-access (MC-CDMA) systems. Generalized DFT filter banks has been traditionally discussed for very high-speed digital subscriber lines (VDSL) wireline systems, received interest also for wireless applications. The design of the generalized DFT modulated filter banks is investigated and its fast implementation is derived in the time-domain for arbitrary integer sampling rate. Through the utilization of the generalized DFT modulated filter banks, one or more subcarriers, even noncontiguous subcarriers can be easily supported by system in both uplink and downlink, which facilitates the users to access the network in a frequency-division multiple-access manner. Simulation results show that the overall bit-error-rate performance of the proposed multicarrier transmission scheme well approaches that of a single-carrier system due to the negligible intercarrier interference introduced by an appropriate design of the generalized DFT modulated filter banks.

In order to increase the bandwidth efficiency and further improve the performance of orthogonal frequency division multiplex (OFDM) systems, adaptive resource allocation and smart antennas techniques are widely applied. However, the employment of fully adaptive beamforming in physical layer for OFDM systems significantly raises the issues in medium access control (MAC) layer, hence affects the implementation of adaptive resource allocation. From a cross-layer approach, we propose a new adaptive resource allocation strategy with hybrid smart antennas for OFDM systems. By applying different smart antennas schemes according to the different quality of service (QoS) requirement of different users, the new strategy reaches a good trade-off between the complexity and the performance of OFDM systems.

Joint channel estimation and symbol detection for space-frequency block coded OFDM (SFBC-OFDM) systems is considered. The expectation-maximization (EM) algorithm is employed to devise both soft-in-hard-out (SIHO) maximum likelihood (ML) iterative receivers and soft-in-soft-out (SISO) maximum a posteriori (MAP) iterative receivers for SFBC-OFDM systems. Besides the low computational complexity and fast convergence, the EM-based iterative receivers also have the ability of tracing the variation of fast fading channels, and thus provide quite satisfying performance and bandwidth efficiency even in high-vehicular-speed environment. Numerical results are provided to corroborate the theoretical designs.

The Doppler shift of the time-varying multi-path channel is estimated by calculating the level crossing rate (LCR) of the signal envelope of the channel coefficient estimates of the strongest path. In order to reduce long observation duration and memory requirements, we recommend to use the 1st order autoregressive (AR(1)) filter. Simulation results show the fast convergence of the proposed algorithm while guaranteeing the estimating accuracy at the same time.

We study the low complexity turbo detector for cyclic prefix based single-carrier block transmission (CP-SCBT) systems with multiple receive antennas. It has the following characteristics: firstly, it can be implemented by FFT/IFFT with low complexity; secondly, along with SISO decoder, turbo detection can be applied. Simulation results show that the iterative receiver provides much better performance than the conventional CP-SCBT system. It also outperforms its coded OFDM counterpart. The most attractive advantage is that it can be implemented by FFT/IFFT without significantly increasing the complexity of the system.

In this paper, we investigate some space-time joint channel estimation (JCE) schemes in filtered multitone (FMT) based multicarrier multibranch (multiuser and/or multiantenna) systems. Each subcarrier is proposed to be processed separately due to the spectral characteristics of the FMT signals On each subcarrier, the wireless channels experienced by all transmit branches are estimated jointly at the receiver. The least square (LS) space-time JCE and weighted least square (WLS) schemes are derived. The constant amplitude zero auto-correlation (CAZAC) code based pilots are proposed for the aforementioned multicarrier applications to reduce the mean square estimation error. Simulation results are provided to validate the theoretical analysis.

Multi-carrier (MC) transmission is seen as the leading candidate for beyond 3G mobile communications. We focus here on the MC scheme known as filtered multi tone (FMT) modulation. We investigate its suitability for an asynchronous uplink multi-user scenario, under the hypothesis of frequency division multiple access (FDMA). In particular, we show the influence of the filter spectral characteristics and the effects of introducing some redundancy in bandwidth through non-critical sampling. Furthermore, we compare the achievable performance with that of an OFDMA system over an AWGN channel in terms of bit error rate.

Within this paper we present a new strategy for applying power control in combination with link adaptation in order to satisfy required quality of service (QoS) parameters and to possibly enhance the overall capacity of HIPERLAN/2 microcellular systems. The efficiency of our algorithm is then investigated and evaluated by means of simulations.

Cellular networks and wireless local area networks (WLAN) are being widely deployed for mobile radio communications. Taking into account the advantageous and drawbacks of both network architectures, it becomes obvious that a combination of them is the logical consequence for future mobile radio networks. The scope of this paper is to introduce a future radio network architecture called hierarchical multihop cellular network (HMCN), which includes several multihop cells. The overlaying cellular network coordinates multihop cells in order to reach an optimal load balance in the whole network. The next evolutionary step towards a HMCN structure is to introduce multihop capable nodes (MHN), which can be fixed or even mobile. The paper shows the challenges and benefits of multihop with fixed nodes, especially the placement of fixed MHN and reduction of radio protocol overhead in order to provide high performance. When MHN are normal mobile nodes, multihop routing becomes a key point in the HMCN concept. The paper proposes a cellular based routing scheme and compares it with the ad hoc routing algorithms being developed by IETF.

The paper defines a radio resource management concept for multimedia services in future broadband mobile radio networks. Based on the HIPERLAN/2 system, we design an adaptive radio resource scheduler which autonomously adapts to current traffic types and volume. We assume IP traffic models for voice, HTTP and video users and optimize the scheduling functions in the access point (base station) of the broadband mobile network in order to maintain QoS for the services. The interworking among admission control, load control and the adaptive scheduler is shown. The principles discussed here are not restricted to H/2 but can be exploited for any radio access technique (RAT) using adaptive schedulers, e.g. dynamic scheduling for reconfigurable terminals.

The paper describes a dynamic classmark scheme based on a finite number of stages during a radio connection procedure for reconfigurable terminals in future multiple radio access technology environments. Based on the user profile, terminal profile and service profile that the user applies, features are clustered into different sets called classmarks. The classmarks are designed in a stage-based manner in order to realize the method of dynamically creating and triggering them. During the reconfiguration, radio link establishment and communication processes, the number of stages is adaptive to the access frequency and priorities of the necessary features required by the network. Thanks to this approach, the signaling burden is highly reduced in the radio network. Therefore, the efficiency of radio resource management is improved.

In January 1998, ETSI (European Telecommunications Standards Institute) determined the air interface standard for UMTS (Universal Mobile Telecomunications System). This standard will comprise the component TD-CDMA (time division CDMA). In this paper, the suitability of TD-CDMA for utilizing intelligent antenna arrays at base station receivers and the benefits achievable by such antennas are demonstrated by simulations. Different types of antenna configurations are studied. The directional channel models needed for the simulations are derived from measured channel impulse responses.