Decision Criterion for Observation-Based Relays in LTE Networks

Abstract

Relay technology has the potential to dramatically improve throughput for Long Term Evolution (LTE) network users. However, the existing 3rd Generation Partnership Project (3GPP) standard for relaying, the Type 1 relay, is best suited to cell extension. An alternative design, Type 2, was considered for increasing throughput within the existing coverage region. It has not been standardized, but has been cited as in need of further study. In this thesis, we augment the Type 2 relay design and achieve the following: 1. Improve throughput for relay-supported users. 2. Empower the relays to make decisions as to which users they support. 3. Introduce as few new protocols as possible to implement the relay. To achieve these objectives, the proposed relay has a decision criterion to compare its own achievable throughput against the throughput of any candidate users it detects. Depending on the relative quality of its connections, the relay may opt to provide two-hop Time-Division Multiplexing (TDM) support or retransmission support. Once it reaches its decision, the relay informs the evolved Node B (eNB) of its intent to support the user and the mode by which it will do so. The eNB adjusts its behaviour accordingly and continues to perform all downlink control functions. Unlike standard relay systems, the proposed approach requires no approval from the eNB and no user handoff. Simulations were conducted using Network Simulator 3.21 (ns-3.21) and data was processed in MATLAB R2012a. For a relay with transmit power characteristics equivalent to users in the cell, 35% to 38% of users within its observation region are eligible for some form of support. The majority of supported users received retransmission support, rather than two-hop TDM. Additionally, if optimized relay placement can achieve a 5 dB improvement to the relay-eNB channel, the percentage of supported users increases to between 49% and 55%. With the 5 dB improvement, the number of users eligible for two-hop TDM increased substantially, particularly at larger bandwidths. Network configuration parameters had a considerable impact on results. In particular, the Control Format Indicator (CFI) and channel bandwidth (W) had the greatest impact on results.