Uplink Joint Detection in a Realistic Macro Cellular Environment
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Beschreibung
The current annual growth rate of mobile traffic is about 70%. One important lever to cope with this demand is increasing spectral efficiency by deploying advanced network technologies. The spectral efficiency in cellular systems is limited by interference from neighboring cells. Inter-cell interference, in systems with independent base stations can only be avoided by increasing the distance at which the frequency is reused. As a result, scarce and expensive resources are wasted as frequency bands are not reused in every cell. Since inter-cell interference particularly impairs communications of users located at cell edges, it also prevents ubiquitous quality of service which to provide is another main objective of mobile operators.
It has been known for quite some time that cooperation among base stations potentially provides a means to solve the interference problem. A very powerful form of cooperation is the joint application of multi-antenna techniques at multiple base stations (in the cellular uplink referred to as joint detection). The benefit of joint detection is backed by a lot of promising theoretic results. However, the models used in this research oversimplify the complex cell coupling and other challenges in the implementation, such as hardware impairments, synchronization, and reliable control signaling. Consequently, they cannot be used for a credible assessment of communications performance in realistic cellular networks. The major testing ground during the standardization of communications methods are sophisticated system level simulations which have, in the past, however, occasionally failed to meet their purpose of accurate performance assessment. Consequently, industry players are cautious about embracing innovations that require costly upgrades of the cellular infrastructure. In order to bring innovations into the communications standards, system complexity and performance need to be assessed under real-world conditions, and simulation studies have to be accompanied by field trials that prove the maturity of a concept and provide reference data.
This thesis investigates the performance of uplink joint detection in a representative large scale testbed. To this end, a reference signal processing design for incorporating joint detection in the LTE uplink is implemented in a prototype system. Using this system, extensive multi-cell and multi-user field trials of joint detection show that spectral efficiency is increased by 50 – 70%, on average. Especially, the performance of cell-edge users is improved (by about 300%) which increases fairness and is a significant step towards ubiquitous quality of service. A comparison of simulation and field trial measurements shows that state-of-the-art models provide accurate prediction of wireless multi-cell propagation. These results prove the accuracy of system level simulations and provide a basis for enhancements of joint detection algorithms and cellular system design in general.
Autor*in
Michael Grieger
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Mobilfunk Uplink Joint Detection, Macro Cellular Environment Zellular