Search

A suboptimum search algorithm that considers the users' power profile in conjunction with a primary stage of polynomial-expanded (PE) linear multiuser detector for mobile uplink is proposed to suppress interference level. The initial stage is improved by mathematical analysis using two new ideas based on the Rayleigh-Ritz and Gershgorin theorems for both synchronous and asynchronous users. The performance of the PE structure is further enhanced by a new suboptimum search algorithm as the second stage. The structure of the search algorithm is based on starting from a point close to the optimum search and performing sequential steps to modify it. The proposed structures of the PE method and the suboptimum search algorithm are well suited together and make them collaboratively work without encountering a high level of complexity, since they use similar information as the correlation matrix. The power profile of the users is also considered in the suboptimum search algorithm, which led to more than a 50% reduction of the complexity, while keeping the performance almost the same. The performance of the final structure is carried out by means of computer simulations, and it has been compared to a partial parallel interference cancellation method with optimized partial coefficients. One of the main features of the structure proposed in this paper is that it performs its operations on the canonical formulation of the system, which makes it highly suitable for a broad range of systems such as multicarrier code division multiple access and multiinput multioutput.

A Low complex interference cancellation via modified suboptimum search algorithm in conjunction with a primary stage of reduced rank linear (RRL) multiuser detector for the mobile uplink is proposed. Initial stage is improved through mathematical analysis via Gershgorin algorithm in linear algebra and RRLG detector is introduced. The complexity of the initial stage is evaluated and compared to the recently reported low-complex Fourier interference cancellation method. Depending on the value of the spreading factor of the active users in system, RRLG outperforms the Fourier algorithm, in terms of complexity. The structure of the RRLG method and the suboptimum search algorithm are well suited together and makes them collaboratively work without encountering a high level of complexity. Considering the power profile of the users in the suboptimum search algorithm leaded to even less complexity, yet keeping the performance almost the same. The performance of the structure is obtained via simulations and has been compared to partial parallel interference cancellation (PPIC) method. A good improvement in performance in the low SNR regions, which is difficult to achieve by conventional multiuser detectors and also important as the actual systems are likely to operate in these regions, has been achieved. All the techniques and their modifications introduced in this work consider the complexity as an important issue that enables them suitable for industry and implementation purposes. Another important feature is that the techniques perform on canonical matrix formulations of the system so they can be applied to MC-CDMA and MIMO systems, as well.

Partial parallel interference cancellation (PPIC) and its adaptive implementation are investigated in this paper. The concept and methodology of the adaptive PPIC implementation is borrowed from the DS-CDMA context. A modification for the adaptive version is also proposed which leads to less complexity and better performance. Different scenarios have been considered to fully investigate the performances in a range of system loading with different combinations of convolutional coding, turbo coding and constellation. The performances are provided in terms of BER, FER, number of active users and in presence of multipath fading channel. They are also compared with the performances of the Equal Gain Combining (EGC) detector. In the low to moderate loadings the PPIC achieves a good performance. High order modulations, on the other hand, deteriorate its performance.

Partial parallel interference cancellation (PPIC) for CDMA mobile communication is known as a powerful method. In this paper, after a brief look at PPIC, a multisensor version of the approach is studied under the UMTS uplink parameters. The performance is evaluated by considering a multipath fading environment and the effect of channel estimation in the receiver. The results are compared with standard RAKE receiver and the differences show a promising gain.