| To satisfy the ever-increasing demand for mobile broadband communications and emerging services, the evolving fifth generation(5G) cellular wireless systems will adopt a multi-tier architecture to serve users with different quality-of-service(Qo S) requirements in a spectrum-efficient manner. This way of deploying more infrastructures is to overlay small cells(e.g. microcells, picocells, femtocells and distributed antennas) on top of existing macrocells, and therefore transforms the conventional macrocell networks into heterogeneous cellular networks(HCNs). As HCNs densify their cell deployment, co-channel interference becomes a major source of obstacles to cell throughput improvement. In addition, cell edge users suffer more from co-channel interference, which may govern end users’ experiences.This dissertation studies management technique of co-channel interference in HCNs. We particularly deal with two aspects of co-channel interference, i.e. the power control and the improvement of spectrum efficiency. According to the power control technology, we have proposed to lower the transmission power by using LDPC codes. Furthermore, we have designed adaptive coded modulation scheme based on RC LDPC codes to maximize the throughput. The main contents and achievements of the research are summarized as follows:(1) In order to study how advanced coding technique lowers transmission power, we compare LDPC code with convolutional code. An iterative sum-product decoding algorithm with 50 iterations has been used to decode LDPC code and a soft Viterbi algorithm has been used to decode convolutional code. The simulation results indicate that both transmission powers and coding gains for LDPC code is very small.(2) According to the power control technology, we have proposed to lower the transmission power by using LDPC codes. To observe interference cancellation with low-power transmission technique, we consider information transmission in a two-user interference channel, i.e. a desired user and an interfering user transmit simultaneously data in the same channel. Two transmission schemes have been assessed for the interfering user, one with convolutional code by high-power transmission and the other one with LDPC code by low-power transmission. The simulation result in a Rayleigh fading channel indicates that if the interfering user uses a LDPC code, BER for the desired user decrease to 1×10-7 at the same SNR.(3) What’s more, according to the throughput problem, we design a high-order adaptive coded modulation(ACM) scheme based on rate-compatible(RC) LDPC codes. The chosen RC LDPC code provides up to 139 code rates with a wide rate range from 0.5 to 0.96. Because 0.96 is the highest rate in RC LDPC codes in the world, the designed ACM scheme can attain the highest throughput. The simulation results indicate that the designed ACM scheme provides a wide throughput from 1 to 5.76 bits/channel.The results indicate that we deploy both RC LDPC codes encoding technique and adaptive coded modulation scheme to maximize the frequency spectrum resources. |
