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EFFICIENT RESOURCE ALLOCATION FOR DOWNLINK CONTROL CHANNEL IN LONG TERM EVOLUTION (LTE)

IP.com Disclosure Number: IPCOM000246279D
Publication Date: 2016-May-23
Document File: 4 page(s) / 22K

Publishing Venue

The IP.com Prior Art Database

Related People

Shiv Prakash: AUTHOR

Abstract

A method is provided that efficiently assigns the Physical Downlink Control Channel (PDCCH) resources and maximizes the number of users that can be scheduled in a given transmission time interval, thereby increasing cell-throughput. While increasing power efficiency, fairness in scheduling opportunity is maintained amongst cell-edge users.

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This is the abbreviated version, containing approximately 41% of the total text.

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EFFICIENT RESOURCE ALLOCATION FOR DOWNLINK CONTROL CHANNEL IN LONG TERM EVOLUTION (LTE)

AUTHORS:

Shiv Prakash

CISCO SYSTEMS, INC.

ABSTRACT

    A method is provided that efficiently assigns the Physical Downlink Control Channel (PDCCH) resources and maximizes the number of users that can be scheduled in a given transmission time interval, thereby increasing cell-throughput. While increasing power efficiency, fairness in scheduling opportunity is maintained amongst cell-edge users.

DETAILED DESCRIPTION

     In the Long Term Evolution (LTE) wireless standard, control channel signaling is done over the Physical Downlink Control Channel (PDCCH). The PDCCH carries downlink scheduling assignments and uplink scheduling grants which contain resource allocation information, transport format information, and hybrid automatic repeat request (HARQ) information. The minimum resource unit allocated to a user for control signaling is called as the control channel element (CCE). Based on the downlink channel quality, the LTE base station can aggregate one, two, four or eight CCEs to construct a PDCCH for a particular user equipment (UE), which corresponds to aggregation levels of 1, 2, 4 or 8. Given the number of limited CCEs allocated to the PDCCH channel, and a number of users to be scheduled in in a given transmission time interval (TTI), the problem arises as to how to maximize the number of users served while ensuring fairness of scheduling opportunity amongst users. This becomes particularly important for cell- edge users which use higher values of aggregation levels to maintain coverage. If proper assignment is not done, high blocking probability of the control channel can be detrimental to system performance.

Copyright 2016 Cisco Systems, Inc.

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    The PDCCH is constructed using a hashing function which defines the candidate CCE sets and their starting positions for different aggregation levels. Because of the pseudo random algorithm used to determine these positions, the candidate positions of several UEs can be overlapping, resulting in blocking of CCEs even if all CCEs are not used. Thus, often there is a possibility that the base station is unable to schedule all users in the current transmitting time interval, even though there are unutilized PDCCH resources. Such users which are not allocated resources for the current TTI are said to be blocked, resulting in less number of users getting scheduled per TTI than what was intended.

    The blocking is more predominant in an interference limited environment and for cell edge users in particular, which are assigned high aggregation levels (to maintain PDCCH Block error rate in low Signal-to-noise-interference ratio (SINR) conditions). The problem is how to efficiently assign the candidate CCEs amongst different users while maintaining low blocking probability, high power efficiency and fairness in scheduling amongst users.

    A comparison is made between performance of a proposed scheduler to a...