Beneyam B. Haile

On Performance Loss of Some CoMP Techniques Under Channel Power Imbalance and Limited Feedback

Spatially distributed transmissions in coordinated multipoint (CoMP) systems can lead to mean channel power imbalance (CPI) at the receiver. Similar imbalance also occurs in distributed antenna and co-located multi-antenna systems due to inaccurate antenna calibration. This paper studies performance impact of power imbalance on some practical CoMP methods with limited feedback. We derive approximate analytical expressions of asymptotic capacity, optimal amplitude weights, as well as signal-to-noise ratio gain for a few methods under analysis. Numerical results validate the analysis and show impacts of erroneous feedback under CPI. Results demonstrate that CPI has significant negative impact on the CoMP performance. Furthermore, our results reveal that amplitude information at transmitter is crucial and detrimental effect of CPI can be effectively compensated by using long-term amplitude information at transmitter. Moreover, additional short-term amplitude feedback shows insignificant gain when a large number of diversity antennas in base stations or CoMP suffer from feedback errors. In fact, a sparsely quantized phase and long-term power information feedback can lead to performance very close to the use of full channel state information at the transmitter.

Use of Coordinated Multipoint Transmission for Relaxation of Relay Link Bottlenecks

The emerging Long Term Evolution-Advanced (LTE-A) standard promises improvements in throughput and reduction in costs-per-bit, through use of techniques, such as, relaying and coordinated multipoint (CoMP) transmission and reception. The inherent self-backhauling of relays nodes makes them an attractive solution in areas where backhaul is either unavailable or costly. However, the performance of the backhaul relay link limits overall performance of relay systems, particularly for relays deployed in the cell edge. In this paper, we propose CoMP-enhancements in order to relax the relay link bottleneck. We study this proposed approach through system simulations of a selected realistic deployment scenario. The results demonstrate that use of a quantized co-phasing (QCP) CoMP technique provides significant signal- to-interference-plus- noise-ratio (SINR) gains and end-to-end throughput improvements for user equipment connected to the relays, even with simple scheduling techniques.

Performance study for off-grid self-backhauled small cells in dense informal settlements

Urban (and suburban) informal settlements in emerging markets will be the fastest growing population hotspots in the next few decades. This presents a significant challenge in delivery of services, including affordable mobile Internet access. Operator-led upgrades through network densification (rollout of additional operator-maintained sites) are difficult to sustain in those areas due to low revenues, lack of fixed lines, energy scarcity, insecurity, and so on. This calls for alternative approaches in mobile network upgrades and operation. In this paper, we present capacity enhancement approach using user-deployed shared-access small cells in the dense informal settlements. To that end, we consider leveraging macro Long Term Evolution (LTE) networks to backhaul High Speed Packet Access (HSPA) small cells. As a case study, we present comparative network simulations based on an example informal settlement. The results of the study highlight the possibilities for cost-effective capacity upgrades for users in dense settlements for even a limited number of unplanned end-user small deployments and self-backhauling via existing macro sites. In the study, we also note possible system performance enhancements of the small cell backhaul link through improved antenna design, scaling of carrier bandwidth and introduction of traffic steering across HSPA and LTE layers.

Coordinateci multipoint transmission for LTE-Advanced networks in dense informal settlements

The emerging Long Term Evolution-Advanced (LTE-A) standard promises improvements in throughput, latency, spectrum-flexibility and reduction in costs-per-bit, through use of techniques, such as, coordinated multipoint (CoMP) transmission and reception. LTE-A enhancements provide an attractive long-term solution for operators to implement cost-effective capacity-upgrades and guarantee affordable broadband access in the emerging markets (e.g., Africa). The fast expanding densely-populated informal settlements are among the key areas that could benefit from this new technology. This paper presents a simulation study on the spectral efficiency gains that are achievable with CoMP transmission in an exemplary dense informal settlement area. The results demonstrate that use of CoMP provides capacity enhancements without need for costly deployment of additional macro sites, thus contributing to affordability of broadband access through reduced cost-per-bit. Moreover, we note possible improvements in energy efficiency, by lowering transmit powers without significant impact on CoMP spectral efficiency gains.

Use of beamforming and interference mitigation techniques for relay backhaul enhancement

Relaying is one of the promising approaches for extending service coverage and improving quality of service. The self-backhauling of relays towards a serving (donor) eNode B provides cost-effective solution for deployment scenarios where conventional backhauling is either costly or unavailable. The end-to-end throughputs achievable by users served by relays are dependent on achievable throughputs on both the relay access and backhaul links. The 3GPP standardized Type 1 inband relay node (RN) employs a time-based resource partitioning between relay backhaul and access links. This resource allocation strategy coupled with sharing of eNode B (eNB) resources between the RN and users served directly by the eNB usually creates a backhaul bottleneck. The relay backhaul link performance is further degraded due to intercell interference, particularly on the cell edge where the deployment of relays are usually targeted. In this paper, the relay users throughput enhancements by relaxation of relay backhaul bottlenecks are investigated through the use of beamforming and interference mitigation techniques. Simulation results demonstrate significant improvements in relay backhaul performance and end-to-end throughputs for relay users through the use of limited feedback beamforming and interference mitigation schemes.

LTE-Advanced enhancements for self-backhauled LTE-U small cells: An Addis Ababa case study

The heterogeneous deployment of high-power macro cells and low-power small cells is expected to become the most common approach for operators to meet the increasing demand for capacity in high traffic areas, such as, dense urban hotspots. Furthermore, the recent proposals for operating Long Term Evolution (LTE) networks in the unlicensed spectrum bands (LTE-U) is being considered as an approach for providing additional spectrum for dense small cell deployments. However, the implementation of affordable and flexible small cell backhaul links remains challenging. To that end, self-backhauling the small cells via the existing macro cells as interesting approach, but has limited capacity compared to traditional dedicated backhaul links. In this paper, we investigate possible performance enhancements through the use of LTE-Advanced enhancements, specifically: coordinated multipoint and carrier aggregation (CA), to relax the downlink backhaul capacity bottleneck for self-backhauled LTE-U small cells. We study this proposed approach through system simulations of a selected realistic deployment scenario in a busy area of Addis Ababa. The results of the simulation campaign demonstrate that deployment of self-backhauled LTE-U small cells in dense urban hotspots can provide notable throughput gains, particularly for the case CA enhancements in the small cell backhaul links.

User association and load balancing in long term evolution network in Addis Ababa, Ethiopia

The exponential growth in mobile data demand is increasing the need for high capacity provisioning. To satisfy this demand, mobile operators are deploying latest generation of cellular technologies, such as Long Term Evolution. Moreover, the non-uniformity in service demand distribution is creating load imbalance on wireless networks. This imbalance reduces the capacity of the networks and various load balancing strategies are being implemented to circumvent it. This paper investigates a geographic load balancing algorithm, called Bubble Oscillation Algorithm in LTE networks and beyond. The BOA is customized to make it feasible in a real LTE network. A realistic test case network in Addis Ababa, Ethiopia, is used to validate the algorithm and compared it with the default LTE user association criteria, the best Reference Signal Received Power. The numerical results show that, BOA improves users throughput at the cell-edge up to 67.1% as compared to the best RSRP. Considering the number of unassociated users as a second criteria for comparison, service outage for BOA is 7.20% while that of the best RSRP is 40.93% when the service demand is equal to total system capacity, which is a significant improvement.