Jong-Han Lim

Link Performance Abstraction for Interference-Aware Communications (IAC)

Advanced co-channel interference aware signal detection has drawn research attention during the recent development of Long Term Evolution-Advanced (LTE-A) systems and the interference-aware communications (IAC) is currently being studied by 3GPP. This paper investigates link performance abstraction for the IAC systems employing maximum- likelihood detector (MLD). The link performance of MLD can be estimated by combining two performance bounds, namely, linear receiver and genie-aided maximum-likelihood (ML) receiver. We propose a new adaptive approach where the combining parameter is adaptively adjusted according to instantaneous interference-to-signal ratio (ISR). The basic idea is to exploit the probabilistic behavior of the optimal combining ratio over the ISR. The link-level simulation results are provided to verify the prediction accuracy of the proposed link abstraction method.

Coding across multicodes and time in CDMA systems employing MMSE multiuser detector

When combining a multicode CDMA system with convolutional coding, two methods have been considered in the literature. In one method, coding is across time in each multicode channel while in the other the coding is across both multicodes and time. In this paper, a performance/complexity analysis of decoding metrics and trellis structures for the two schemes is carried out. It is shown that the latter scheme can exploit the multicode diversity inherent in convolutionally coded direct sequence code division multiple access (DS-CDMA) systems which employ minimum mean squared error (MMSE) multiuser detectors. In particular, when the MMSE detector provides sufficiently different signal-to-interference ratios (SIRs) for the multicode channels, coding across multicodes and time can obtain significant performance gain over coding across time, with nearly the same decoding complexity.

Performance analysis of fixed cell assignment in broadband wireless networks

The analytic model and computer simulation used in this paper evaluates performance in terms of the throughput of a dynamic channel allocation method, called the fixed cell assignment (FCA). The FCA employs packet switched time division multiple access transmission for the forward link in broadband (10 Mbit/s) wireless networks at the operating frequency 2 GHz. Regarding the analytic model, throughput of the base station is obtained using a Markovian queueing model at M/M/1/K state for a single first-in-first-out (FIFO) buffer with finite capacity and the concept of the carrier-to-interference ratio. If the buffer is full when a new packet arrives, the packet is blocked and cleared. The blocked packet should be retransmitted from the mobile node. Using the power controlled interference model, the specific model for throughput is obtained through the probability of the successful packet transmission in a time slot. Computer simulation shows the relationship between the throughput and the blockage probability.