Performance Of WCDMA System Research Articles

Channel Equalization of WCDMA Downlink System Using Finite Length MMSE-DFE

The performance of WCDMA system deteriorates in the presence of multipath fading environment. Fading destroys the orthogonality and is responsible for multiple access interference (MAI). Though conventional rake receiver provides reasonable performance in the WCDMA downlink system due to path diversity, but it does not restores the orthogonality. Linear equalizer restores orthogonality and suppresses MAI, but it is not efficient, since its performance depends on the spectral characteristics of the channel. To overcome this, Minimum Mean Square Error- Decision Feedback Equalizer (MMSE-DFE) with a linear, anticausal feedforward filter, causal feedback filter and simple detector is proposed in this paper. The filter taps of finite length DFE is derived using the cholesky factorization theory, capable of suppressing noise, Intersymbol Interference (ISI) and MAI. This paper describes the WCDMA downlink system using finite length MMSE-DFE and takes into consideration the effects of interference which includes additive white gaussian noise, multipath fading, ISI and MAI. Furthermore, the performance is compared with conventional rake receiver and MMSE and the simulation results are shown. Keywords - MMSE, MMSE-DFE, rake receiver, WCDMA

Performance of W-CDMA systems with rectangular signalling in OSTBC MIMO generalised Nakagami- m fading channels

The performance of combined temporal multipath diversity with statistically independent branches and spatial antenna diversity with arbitrarily correlated branches is investigated. A downlink wide-band code-division multiple access system employing orthogonal space-time block coding multiple-input-multiple-output communications is considered. The performance is quantified in terms of the average symbol error probability (SEP) of coherent arbitrary rectangular quadrature amplitude modulation in Nakagami-m fading with arbitrary statistics. Through the analysis, new expressions for the average SEP are derived under the generalised system model described above. Specifically, the considerations of the combined path and space diversity model, the arbitrary correlation profile among spatial diversity branches, and the arbitrary statistics of Nakagami-m fading processes are the main aspects that make the system model herein generalised as compared to previous ones. Furthermore, for this generalised system model, the consideration of distinct in-phase and quadrature decision distances as well as modulation orders in the rectangular signalling constellation through the analysis provide additional enhancements on some existing results. Numerical and simulation results are presented to demonstrate the enhanced validity of the analytical development.

Analysis of TFCI coding performance of WCDMA systems

In WCDMA system, transport format combination indicator (TFCI) is encoded by an encoder based on Reed-Muller code and transmitted in a time-multiplexed fashion. When the number of TFCI information bits is less than the number of input bits to encoder, subset of basis sequences should be used. In this paper, we analyze the upper bound of word error rate (WER) of TFCI coding and find the optimal subset of basis sequences that minimize the bound. Since the bound of the WER is dependent on the channel correlation, the basis sequences to mitigate the effect of channel correlation are selected. From the result, a basis sequence with uniformly distributed bit of '1' is firstly chosen in optimal subset of basis sequences. The choice of basis sequences is more significant for high mobile speed.