Research in LTE-A
Networks Research Group
Department Of Computer Science
University of California Davis, USA
'Cross-layer Coordination for Efficient Contents Delivery in LTE eMBMS Traffic'
Authors: E. Baik, A. Pande and P. Mohapatra
Summary: This work utilizes the idea that joint prediction of Raptor code rate and HARQ retransmissions can lead to savings in redundant information in a cellular network.
Abstract: Evolved Multimedia Broadcast Multicast Services (eMBMS) in LTE standards provides Raptor code as Forward Error Correction (FEC) scheme in application layer. Hybrid automatic repeat request (HARQ) is also used to increase reliability at MAC layer for packet recovery. The two mechanisms, with no interactions between them, may either lead to more redundancy in download link (DL) network resource or meaningless drops of recovery data at application layer. In this paper, we first analyze tradeoff between two recovery mechanisms and then present a probabilistic model to find optimal Raptor encoding rate and number of HARQ retransmissions for a given network condition. This can achieve a saving of upto 13-15% in DL network resources compared to existing schemes while ensuring reliable file delivery. It was also found to reduce the transmission delay (by minimizing the number of re-transmissions). The model was evaluated using LTE-A simulation framework..
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'Edge-prioritized Channel- and Traffic-aware Uplink Carrier Aggregation in LTE-Advanced Systems'
Authors: R. Sivaraj, A. Pande, K. Zeng, K. Govindan and P. Mohapatra
Summary: In this work, we propose grouping of UEs prior to Radio-resource management. This grouping is very useful to give efficient representation to edge users who are prioritized to give good component carriers. Carrier Aggregation is used to ensure required bitrates to each group.
Abstract: Carrier Aggregation (CA) in LTE-Advanced yields higher data rates to the User Equipments (UE). The existing schemes for CA lack channel-awareness leading to unfair allocation and aggregation of carriers to UEs.The cell-edge users particularly suffer from exhaustion of resources, higher fading losses, lower SINR values (and hence higher power consumption in uplink) and channel-blind assignment often implies that their traffic requirements are least satisfied. This paper addresses the above concern by proposing an edge-prioritized channeland traffic-aware uplink CA comprising of Component Carrier (CC) assignment and resource scheduling. The LTE-A UEs are spatially grouped and the under-represented groups (such as the ones comprising edge UEs) are prioritized for CA. This results in assigning the best channels to the edge groups. The Physical Resource Blocks (PRBs) are assigned to the groups based on Proportional Fair Packet Scheduling (PFPS) in the time domain while frequency domain PFPS is used to address resource contention amongst individual UEs in a group. The proposed approach outperforms the existing channel-blind and opportunistic RRM techniques by 33% in CC assignment and 21% in PFPS.
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