Blind turbo channel estimation in OFDM receivers

Finite-Alphabet-based blind channel estimation in OFDM systems is known to be extremely complex due to an exhaustive search to be performed over a tremen-dous number of channel coe±cient combinations. In this paper, we present a novel blind channel estimator which dramatically reduces this number of coe±cient combinations to be checked without a signi¯cant dete-rioration in estimation quality. Hence, the new low complexity approach enables the application of blind channel estimators based on the ¯nite alphabet set even if the transmitted data are high-rate modulated. Fur-thermore, we show that the performance of blind chan-nel estimation can be improved by an iterative process based upon the capabilities of channel coding. Using bit error rates, the algorithm is tested with simulations and compared to other blind and nonblind channel es-timators.

Noncoherent RAKE-Receiver with Optimum Weighted Combining and Improved Closed-Loop Power Control

2 : In this paper, we present two methods to improve the performance of a mobile communication system compatible to the standard IS95. The first approach reduces the bit error rates by modifications of the closed-loop power control scheme. In order to overcome the detrimental effects of delayed control information, linear prediction is used. This is especially helpful at higher velocities of the mobile user. Secondly, we apply weighted combining of correlation components in the demodulation process within the RAKE receiver. 1 Introduction D IRECT sequence code division multiple access (DS--CDMA) is an attractive candidate to be considered for future mobile communication applications. It is regarded as a promising technique to increase the capacity of cellular mobile radio systems. In 1993 the standard IS-95, also called QUALCOMM--CDMA, was adopted in the USA [1]. Here, we use this standard as a basis to improve system performance in the uplink by means of optimized components. To r..

BER Analysis of a Novel Hybrid Modulation Scheme for Noncoherent DS-CDMA Systems

A novel DS-CDMA transmission scheme combining the two well-known techniques of M-ary orthogonal and differential PSK-modulation is presented. This "hybrid" scheme is applicable to the noncoherent uplink of the IS-95 system where up to now only M-ary orthogonal modulation is used. The additional, PSK-modulated data show a slightly increased bit error rate (BER) compared to the data from M-ary modulation. However, the overall degradation caused hereby is far outweighed by the gain achieved by a higher spreading factor. Analytical results confirmed by simulations yield an improvement of approximately 1:0 dB in terms of ¯ E b =N 0 on a Rayleigh fading channel when no channel coding is used. This considerable gain is achieved upon only slight modification of the conventional modulation/demodulation procedure at a low additional complexity. It will be demonstrated that the IS-95 system is not properly designed since the full exploitation of noncoherent demodulation techniques results in a ..

A New CDMA-Concept using Hybrid Modulation with Noncoherent Detection

2 : In this paper, we present a novel transmission scheme with application to Direct Sequence Code Division Multiple Access (DSCDMA) combining M-ary orthogonal and PSK modulation. With this "hybrid" modulation procedure, additional data is transmitted in the phase of each M-ary symbol. Note that it is due to real valued symbols that this transmission capacity is lost in state-of-the-art communication systems. The bit error probability is derived for both PSK and DPSK as the additional modulation type for an AWGN channel. The analytical results are confirmed by simulations. Finally, we show that the hybrid scheme is applicable to the noncoherent reverse link of the American IS-95 system by introducing an additional DQPSK. 1 Introduction C ONVENTIONAL M-ary modulation schemes such as M-ASK (M-ary amplitudeshift keying) or M-PSK (phase-shift keying) are defined by their complex signal space representation. With the use of direct sequence spread spectrum techniques (DS-SS) it is possible..