| With the wide spread of Mobile Intelligent Terminal, the higher speed and larger capacity is needed for future communication. However, the low frequency band of the radio spectrum resource is crowded nowadays. Therefore, researchers pay more attention to the high frequency band communication. In 2013, China opened the band 42.3-47.0GHz and 47.2-48.4GHz to develop Chinese wide band wireless communication. In September 2012, the task group TGaj under IEEE 802.11 was formally established. This amendment defines modifications to the PHY and MAC layers to enable the operation in the Chinese 60 and 45GHz frequency band. This thesis focuses on 45 GHz baseband algorithms and framework for IEEE 802.11aj PHY and MAC which is being standardized. And simulations are maded to analyse the system performance.Firstly, the characteristic of 45GHz channel environment is investigated. Then the IEEE 802.11 aj channel model which has correctly described path loss, shadowing and power delay profile is established to lay a foundation for the subsequent research.Secondly, LDPC encode and STBC techniques for single carrier modulation are investigated. According to the code rate, the structured LDPC code is well designed. Besides, LDPC encoding and decoding algorithm are investigated for data field. Besides, an enhanced log-likelihood ratio (LLR) calculation method based on a simple SNR estimation is given in this thesis. The method takes FFT, FDE and IFFT into consideration, thus facilitates the LDPC decoding in SC. In single carrier system which supports several space streams, we propose a low-complexity STBC algorithm combining Alamouti with single-carrier frequency-domain equalization. Simulation results show the STBC technique in time domain has gain more performance compared with CSD when signaling with higher order constellations as the complexity of the equalizer is not increased.Thirdly, the PHY layer design for IEEE 802.11aj and hardware impairments are investigated. In the physical (PHY) layer design, there are two competitive techniques. One is orthogonal frequency division multiplexing (OFDM) and the other is single carrier modulation. Both systems are designed at transmitter and receiver. Finally, the performance of OFDM and SC under hardware impairments including non-linear distortion in power amplifier and phase noise is compared. The simulation results suggest that the SC system is a hardware-friendly technology and has much better performance than OFDM under hardware impairments, thus SC is much more promising for the emerging Multi-Gbps WLAN (IEEE 802.11aj) standardFinally, this paper investigate the channel access techniques which can be used in the MAC layer for IEEE 802.11aj. Motivated by the results on fairness, this thesis solved the collision problem of RTS/CTS access mechanism. According to the CTS frame received, Stations around set their NAV values reasonably. Simulation results show that the solution has greatly improved the system fairness especially when the network load is busy. Existing backoff scheme of DCF consider only saturated conditions. Based on the real situations, this thesis proposed a dynamic adjusting algorithm for the initial value of contention window. The algorithm uses a new method to estimate the number of competing stations at AP first, and then adjusts the initial value of contention window dynamically. Simulation results show that it has improved the backoff scheme’s sensitivity to traffic intensity and increased the throughput as well with a few modifications of the protocol. |
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