MIMO-OFDM channel estimation: a pilot sequence design for time-domain processing

A pilot sequence design for MIMO-OFDM systems is investigated where all transmit antennas share the same sub-carriers to convey pilot symbols. The pilot sequences are endowed with phase-shifting properties, granting the receiver the possibility of extracting the impulse responses for all channels directly from the antennas’ time-domain received signals, without co-channel interference. A linear processing of the timedomain samples is all that is needed to get the channel impulse responses, resulting in an algorithm with very low computational load. The feasibility of the investigated method is substantiated by system simulation using indoor and outdoor broadband wireless channel models

Performance of extended space-time coding techniques for MIMO MC-CDMA systems

In this paper we consider a transmission system based on MC-CDMA, where signal spreading is performed entirely in the frequency domain. An extended spacetime coding technique, the Double Alamouti, is evaluated considering a MIMO channel. This assessment is made against standard Alamouti coding, for two different Tx/Rx antenna schemes (2x1 and 2x2). Numerical results, attained through system model simulations, are presented for performance evaluation under realistic scenarios considering some typical system impairments. These results show that in practical systems significant improvements can be achieved by using the Double Alamouti coding scheme

TCM coding of PPM based modulations for Infrared WLAN's impaired by ISI

In this communication we consider the use of PPM based modulation methods, such as the hybrid modulation method called Amplitude and Pulse-Position Modulation (APPM) and Overlapping Pulse-Position Modulation (OPPM) to improve the performance of infrared WLAN’s, by the use of Trellis-Coded Modulation (TCM) codes. We describe the best code search and results, which demonstrate that, even with trellis codes of moderate complexity, non-negligible coding gains can be obtained without bandwidth expansion. Monte Carlo simulations have been done to compare uncoded PPM against APPM and OPPM TCM coded systems performances, on ceiling-bounce channel models for various values of delay spread. Although our codes were derived for the AWGN channel without Inter-Symbol Interference (ISI) awareness, their behavior in multipath dispersion channels is quite effective

Simulation-based evaluation of spectrum opportunities in UMTS cellular networks

A scenario based on an UMTS TDD opportunistic cellular system that operates over UMTS FDD licensed cellular networks is considered. Therefore we develop a simulation tool that addresses the goal of analysis and assessment of UMTS TDD opportunistic radio system in a coexistence environment with UMTS FDD primary cellular networks. The communication presents the scenario considered, the main features of the tool, discusses and proposes metrics to evaluate the communication opportunities in UMTS FDD primary cellular networks, and presents numerical simulation results. These show that a moderate number of UMTS TDD available frequencies and a reasonable UMTS TDD opportunistic radio transmission power will allow the deployment of UMTS TDD opportunistic radio networks in a coexistence environment with existing licensed systems

Direct time-domain channel impulse response estimation for OFDM-based systems

A method to estimate the channel impulse response using the received serial data in time-domain, without using DFT operations, is investigated. The processing required by the proposed method is substantially reduced when compared with LS-DFT channel estimation method, with no performance degradation. Furthermore, this method can incorporate the results of other published works that are DFT-based, at little or no added complexity, to improve the estimate of channel impulse response

Vectorial channel estimation for uplink MC-CDMA in beyond 3G wireless systems

In beyond 3G wireless systems the bandwidth efficiency can be increased with the use of adaptive antenna arrays. This paper focus on a key issue for adaptive antenna arrays, that is, channel parameters estimation including Direction-Of-Arrival (DOA). In order to estimate DOA. the channel frequency responses for the links between the mobile users and each of base station array elements are estimated by pilot-aided minimum mean square error (MMSE) algorithm. This estimator is not sensitive to the channel statistics. Based on frequency response estimatives DOA's of impinging multipath components to the base station are estimated by a low complex Wlauimuni Likelihood (ML) approach. Furthermore an uplink burst structure with specifically designed midamble field for multiuser channel estimation in MC-CDMA is proposed. The performance is assessed in terms of channel estimation errors for a MC-CDMA TDD system over fast and slow fading mobile channels

Baud sampling bit synchroniser for channels with data dependent noise

A bit synchronisation algorithm for channels with data dependent noise which operates with one sample per symbol is presented. The algorithm uses the same information as the Mueller and Muller (M&M) algorithm, and is optimised for operation with data dependent noise. The performance is derived and it is shown that signfkant improvements over the M&M algorithm can be obtained in practical optical channels

Application of SDMA with scheduling for MIMO MC-CDMA

Incoming Beyond 3G systems provides high data rates by using several techniques including Beamforming. Convenient DRA design is required to optimize the capabilities offered by smart antennas. This paper is to presents a DRA algorithm based on the HSDPA of UMTS, including scheduling that exploit SDMA technique that was implemented in the ambit of the IST 4MORE project. Results shown cell throughput gain of SDMA compared to sectorized cells about 76%, and that SDMA gain will increase with user diversity within the cell

High resolution DOA estimation technique for uplink TDD mode

This paper investigates a maximum likelihood (ML) approach for direction of arrival (DOA) estimation based on the algorithm suggested by the 3GPP for scalar channels in UTRA-TDD mode. The performance of the algorithm is assessed by resorting to simulations in typical UMTS scenarios. The results indicate that the proposed scheme overcomes the limitation of the angular resolution inherent to classical techniques like subspace or beam-forming methods. In particular, it is shown that waves exhibiting an arbitrarily small difference in azimuth and temporal spacing higher than one chip time interval can be easily separated. A threshold operation is included to select only the most significant paths, in terms of energy, of the estimated channel. The results show that a good performance can be achieved from low to high values of Eb/N0

Distributed antenna systems aspects and deployment

A lot of schemes are proposed to exploit the transmit diversity. Distributed antenna systems (DAS) constitute one of the most attractive schemes to efficiently achieve the stringent quality of service demands of next generation wireless networks. In this paper, we investigated MISO assisted different transmission techniques used in DAS and the performance of downlink multi-cell DAS in terms of capacity improvement using SINR for different transmission scheme. A system level simulation tool is used to analyze the performance