Opportunistic Downlink Scheduling in Femto Abss
IEEE C802.16m-09/ 2426
Project / IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16Title / Opportunistic downlink scheduling in Femto ABSs
Date Submitted / 2009-11-06
Source(s) / Byung Moo Lee, Sang-Kyu Woo, Kwang Jun Ha, Jeong-Hwi Kim, Jong-Sik Lee, and Seong-Choon Lee
KT
Sung-Yeop Pyun, Helena W, Yong Jin Kwon and Dong-Ho Cho
KAIST
Howon Lee and Bang Chul Jung
KI ITC / E-mail:
E-mail:
E-mail:
Re: / Call for Letter Ballot # 30a on “ P802.16m/D2” (15.7 Support for Self-organization)
Abstract / Opportunistic downlink scheduling to achieve reduced interference
Purpose / Proposed to be discussed and adopted by TGm
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Opportunistic downlink scheduling in Femto ABSs
Byung Moo Lee, Sang-Kyu Woo, Kwang Jun Ha, Jeong-Hwi Kim, Jong-Sik Lee,
and Seong-Choon Lee
KT
Sung-Yeop Pyun, Helena W, Yong Jin Kwon and Dong-Ho Cho
KAIST
Howon Lee and Bang Chul Jung
KI ITC
1. Introduction
Since a large number of Femto ABSs can be installed in the coverage of an overlay Macro ABS by users without cell planning of service providers, interference between Macro ABSs and Femto ABSs causes a severe problem. In a dense environment, in which many Femto ABSs exist in a small region and a great portion of the Femto ABS is overlapped by other Femto ABSs, interference between adjacent Femto ABSs causes a large performance degradation of the Femto ABSs.
In general, there exist two kinds of methods to mitigate the interference between Femto ABSs: 1) power control; 2) resource reservation and sharing. On the control method, the Femto ABS reduces its transmission power to mitigate interference to neighbor cells. For this method, it is hard to guarantee QoS (Quality of Service) of AMSs (especially, in cell edge) and convergence in the transmission power of Femto ABSs. On the resource reservation and sharing method, the interference can be mitigated by static or semi-static radio resource reservation and resource sharing using FDM or TDM manner. For this method, there exists no interference but spectral efficiency decreases
2. Proposed method
In this contribution, we propose an opportunistic scheduling scheme for the operation of Femto ABSs which makes groups of Femto ABSs and allocates radio resource (e.g. sub-frame) to the groups to mitigate the interference between Femto ABSs. Femto ABSs in the same group can share the allocated resource while guaranteeing QoS of AMSs.
The grouping method which minimizes the interference between adjacent Femto ABSs is proposed as shown in Fig. 1. When new Femto ABS is installed, the Femto ABS performs scanning to find neighbor Femto ABSs. Based on the received signal strength from the neighbor Femto ABSs, the Femto ABS estimates interference from each neighbor Femto ABS and reports the estimated interference to SON sever. Then, SON server checks whether interference from neighbor Femto ABSs in each existing group is above a threshold value which is related to QoS of AMSs in cell edge. If the interference from the existing group is smaller than the threshold, the Femto ABS can share the same resource with neighbor Femto ABSs in the existing group while QoS of AMSs can be guaranteed. Therefore, the Femto ABS joins the existing group as a member of the group. If the interference from existing groups is larger than the threshold, the Femto ABS cannot share the same resource with neighbor Femto ABSs in the existing groups because QoS of AMSs cannot be guaranteed. Therefore, SON server makes a new group which contains only new Femto ABS.
When groups are updated, for each group, SON server controls the transmission power of Femto ABSs in the same group to optimize the network performance, coverage and capacity of the Femto ABSs. In the proposed scheme, since the power control is performed among only Femto ABSs in the same group not all adjacent Femto ABSs, it is relatively simple to guarantee the convergence of Femto ABSs’ transmission power.
Figure 1 Grouping method
An example of Femto ABS grouping is shown as Fig. 2 in which four Femto ABSs are installed in order (from Fetmo ABS #1 to Femto ABS #4). When Femto ABS #1 is installed, there is no neighbor Femto ABS. Therefore, SON sever makes a new group {1} which contains newly installed Femto ABS #1. When Femto ABS #2 is installed, interference from Femto ABS #1 in the existing group {1} is smaller than the threshold. Therefore, Femto ABS #2 joins the existing group {1} and hence the group {1} is updated to group {1,2}. When Femto ABS #3 is installed, the sum of interference from Femto ABS #1 and #2 in the existing group {1,2} is larger than the threshold. Therefore, SON sever makes a new group {3} which contains newly installed Femto ABS #3.When Femto ABS #4 is installed, the interference from Femto ABS #3 in the existing group {3} is larger than the threshold. In addition, the sum of interference from Femto ABS # 1 and #2 in the existing group {1,2} is smaller than the threshold. Therefore, Femto ABS #4 joins only the existing group {2,3} and hence the group {2,3} is updated to group {2,3,4}.
(a) Femto ABS #1 is installed
(b) Femto ABS #2 is installed
(c) Femto ABS #3 is installed
(d) Femto ABS #4 is installed
Figure 2 Example of Femto ABS grouping
When groups of Femto ABSs are formed, SON server allocates radio resource to each group as shown in Fig. 3. In the example, there exist four groups of Femto ABSs, {1,2}, {1,4}, {2,4}, and {3}. SON server collects the cell load information of Femto ABSs (e.g the number of active users, traffic queue length) periodically. Based on the collected information, SON server allocates radio resource to the groups adaptively with a period of scheduling round, TR. In the example, the scheduling round TR. is set to 2 super frames. Each super frame consists of 4 subframes. The sum of downlink queue length of Femto ABSs in each group is 2 for group {1,2}, 2 for group {1,4}, 2 for group {2,4}, and 2 for group {3}, respectively. Therefore, the number of subframes allocated to each group is 2 for group {1,2}, 2 for group {1,4}, 2 for group {2,4}, and 2 for group {3}, respectively.
Figure 3 Example of scheduling Femto ABS groups
Text Proposal for the IEEE 802.16m
======Start of Proposed Text ======
15.7.3 Self Optimization
15.7.3.1 Support of Interference Mitigation
SON server may make groups of Femto ABSs and allocate radio resource to each group with object to mitigate interference between adjacent Femto ABSs. Femto ABSs in the same group can share the allocated resource while guaranteeing QoS of AMSs. SON server may control the transmission power of Femto ABSs in the same group to optimize the network performance, coverage and capacity of the Femto ABSs.
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