一種新穎的針對(duì)單小區(qū)點(diǎn)對(duì)多點(diǎn)e-MBMS業(yè)務(wù)傳輸技術(shù)

張碧軍，李亞麟，王偉，蔣智寧，林凌峰

（上海貝爾股份有限公司W(wǎng)SPD無(wú)線事業(yè)部，上海201206）

一種新穎的針對(duì)單小區(qū)點(diǎn)對(duì)多點(diǎn)e-MBMS業(yè)務(wù)傳輸技術(shù)

張碧軍，李亞麟，王偉，蔣智寧，林凌峰

（上海貝爾股份有限公司W(wǎng)SPD無(wú)線事業(yè)部，上海201206）

多媒體廣播多播業(yè)務(wù)（MBMS）是3GPP-R6版本中定義的一種典型的廣播、多播業(yè)務(wù)。隨著技術(shù)的演進(jìn)，在LTE系統(tǒng)中提出了增強(qiáng)的MBMS，即e-MBMS業(yè)務(wù)。針對(duì)e-MBMS業(yè)務(wù)，提出了一種有效的技術(shù)解決方案。該方案可看作下行發(fā)射分集、基于DoA的波束賦形與HARQ技術(shù)的結(jié)合。同時(shí)，仿真結(jié)果也表明，該方案相對(duì)于單獨(dú)的發(fā)射分集來(lái)說能帶來(lái)顯著的性能增益。

增強(qiáng)的多媒體廣播多播業(yè)務(wù)；長(zhǎng)期演進(jìn)；波束賦形；波達(dá)角；發(fā)射分集；混合自動(dòng)請(qǐng)求重傳

1 Introduction

Multimedia broadcast/multicast service（MBMS）is one of the key features in 3GPP Release 6/7/8 and has been typically deployed under two scenarios，i.e.，singlecell and multi-cell point-to-multipoint transmission.With the evolution of technology，enhanced MBMS，i.e.，evolved（e）-MBMS has also been defined in long term evolution（LTE）.For single-cell scenario，some advanced physical layer technologies，e.g.，link adaptation，hybrid-ARQ（HARQ）and closed-loop MIMO，etc.could be used due to some signaling feedback over the air from terminals to the evolved NodeB（e-NB）［1］.

As one advanced closed-loop MIMO technology，beam-forming is often used to improve the throughput［2－3］of cell edge users，thus enhancing the cell coverage in LTE system.Up to now，both kinds of downlink beamforming technologies have been extensively discussed in 3GPP for unicast point-to-point transmission［4－6］.The first one is downlink beam-forming based on uplink feedback and the other one is downlink beam-forming based on uplink estimation.

For single-cell point-to-multipointe-MBMS transmis-sion in LTE system，there aremany papers to discuss the beam-forming operation.Among those papers［7－8］，the main disadvantages could be summarized as the following two aspects.The first one is that uplink signaling feedback is overloaded.Various channel information，e.g.，long-term channel correlationmatrices or short-term channel state information need to feed back from all terminals to e-NB.The other one is to usemax-min principle under beam-forming operation.If following themax-min policy，receiving performance of other users will be sacrificed to improve the performance of thatworst-case user.As a result，the final cell average throughputwill be decreased.

In this paper，in order to overcome above drawbacks，on the one hand，try to reduce largely the uplink signaling feedback，on the other hand，try to use efficiently the downlink beam-forming operation，a novel scheme for single-cell point-to-multipoint e-MBMS transmission in LTE system is proposed.

2 Proposed Algorithm

For single-cell point-to-multipointe-MBMS transmission，themost typical characteristic of point-to-multipoint operation is thatalle-MBMSsubscribed users in the serving cell will receive the same service contents from the downlink common time-frequency resources at the same time.Thus，any downlink transmission policy will affect all the e-MBMSsubscribed users.Different from previous pure beam-forming operation，here to the 1st initial transmission，use open-loop transmit diversity.When deployed by multiple transmit antennas e.g.，4 or 8 at e-NB，transmit diversity could form wider beam thus improving the receiving performance of large e-MBMS users.After the 1st initial transmission，theremay be some users still need to do retransmission.To those retransmission users，use downlink beam-forming to improve receiving performance and decrease retransmission probability.In order to explain this idea clearly，the detailed operation procedure is addressed as follows.

（1）Downlink multiple antennas，i.e.，2，4 and 8 are deployed at e-NB as shown in Figure 1.Here assume uniform linear antenna array at e-NB.

（2）For the 1st initial transmission，use those antennas denoted in stippled in Figure 1，thus，arrive at full rate by using orthogonal space-time or space-frequency coding（SFBC）.

（3）Dual thresholds：high signal interference noise ratio（SINR）threshold and low SINR threshold have been pre-determined at e-NB and signal to all interested e-MBMSusers.

（4）To those users whose received SINR is already higher than that pre-determined high SINR threshold，it denotes that the receiving performance already satisfies their quality of service.Thus，no any retransmission is needed.To those userswhose received SINR is lower than that low SINR threshold，it denotes even if have toomuch retransmission，it is still not decoded right.So，from terminals perspective，only those userswhose receiving SINR located between the dual thresholds need to feedback signaling to e-NB.

（5）At e-NB side，only those userswho feedback uplink signaling do estimation of departure of angle（DoA）using all uplink receive antennas.

（6）During HARQ retransmission，use downlink beam-forming to aim at that worst-case user among those feedback users.For the downlink beam-forming，use DoA based algorithm to form narrow beam to improve the receiving SINR of thatworst-case user.

（7）When the maximum retransmission number has been achieved or there are no users between the dual thresholds，go back to step（1）.

Fig.1 Downlinkmulti-antennas configuration圖1下 行系統(tǒng)多天線配置

Themain advantages of this proposed schemeare are described as follows.

（1）It is applicable to any transmit antenna number.

（2）Uplink signaling overhead could be largely decreased due to the configuration of those dual SINR thresholds.

（3）For the 1st initial transmit diversity based transmission，the larger antenna spacing denoted in Figure 1，especially under 4 and 8 transmit antennas，will result in low spatial correlation and improve the transmit diversity performance.

（4）Beam-forming happens only during HARQ retransmission and it will improve the receiving SINR of thoseworst-case users but does not incur performance loss of others.Also，itwill decrease the retransmission probability by beam-forming operation.

3 Simulatioin and Analysis

In order to verify the proposed scheme，system-level and link-level simulation parameters and corresponding simulation resultswill be provided in this section.

3.1 Relevant parameter settings of system and link level

In table 1，the system-level and link-level simulation parameters have been given.

Table 1 Parameter settings表1參數(shù)設(shè)置

In simulation，assume all users dropped randomly and uniformly in each cell.Do notmodel spatial correlation at receiver due to that wider antenna spacing.Ideal DoA values are used in the simulations and EESM［9］mapping algorithm from system-level to link-level is used to calculate the final effective SINR.

3.2 Simulation results

For convenient comparison，the cumulative distribution function（CDF）of effective SINR for 2 transmit and 2 receive antennas（denoted by 2×2 in Figures）O-SFBCwithout HARQ（“wo”denotingwithout HARQ and“w”denoting with HARQ in Figures）is presented in Figure 2 for basis.

From Figure 2，it is clearly shown that the working intervals of SINR are［－25－15］dB at90％coverage operation point.Thus，in latter simulation，the dual SINR thresholds are set as［－23－16］dB and they are easily to be modified to adapt to different coverage requirements.

Fig.2 CDF of effective SINR for 2×2 O-SFBCwo HARQ圖2 2×2空頻編碼無(wú)HARQ重傳系統(tǒng)有效SINR的累積分布

The proposed scheme，denoted as“BF w HARQ”under two antenna configurations，4×2 and 8×2 have been simulated.Here BF is an abbreviation of beamforming.As basis，2×2 O-SFBC w/wo HARQ has also been simulated.The detailed comparison on SINR with three user number，6，10 and 14 are respectively presented in Figure 3～Figure 5.

Fig.3 SINR comparison under 6 users圖3 6個(gè)用戶的SINR對(duì)比

Fig.4 SINR comparison under 10 users圖4 10個(gè)用戶的SINR對(duì)比

Fig.5 SINR comparison under 14 users圖5 14個(gè)用戶的SINR對(duì)比

Observed at90％coverage operation point from Figure 3～Figure 5，the performance comparison between the proposed scheme and 2×2 O-SFBCw/wo HARQ is summarized in Table 2.

Table 2 Performance comparison表2性能對(duì)比

From Table 2，the following observations could be found.

（1）Retransmission probability：comparing“4×2/8 ×2 BFwith HARQ”and“2×2 O-SFBCw HARQ”，the network average retransmission probability decreases about 30％or so under three user number.Since beam-forming happens only during HARQ retransmission，it will improve largely the receiving SINR of those retransmission users，thus decreasing the final retransmission probability.With the increase of transmit antenna from 4 to 8，the retransmission probability decreases more since the narrower beam under 8 antennas will focus efficiently transmission power at that worst-case user，equivalently，improve the final receiving SINR.

（2）SINR gain：comparing“4×2/8×2 BF with HARQ”and“2×2 O-SFBCwo HARQ”，almost 4.5 dB gain will be achieved.The gain is also benefited from the beam-forming operation during HARQ retransmission. Observed from Figure 3～Figure 5，the average SINR gain from the proposed scheme could be found even compared with“2×2 O-SFBCw HARQ”.

4 CONCLUSIONS

An efficient scheme applicable to single-cell pointto-multipoint e-MBMS transmission in LTE system has been proposed in this paper.This novel scheme could be seemed as the combinations of downlink open-loop transmit diversity，DoA based beam-forming and HARQ retransmission.From the system-level results，the retransmission probability compared“4×2/8×2 beam-forming with HARQ”with“2×2 O-SFBC with HARQ”could be reduced by 30％or so.The SINR gain is about 4.5 dB or so at90％coverageworking point compared with“2× 2 O-SFBC without HARQ”.Even compared with“2×2 O-SFBC with HARQ”，the average SINR gain can also be found from system-level simulation.

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Biography：

ZHANG Bi-jun was born in Bazhong，Sichuan Province，in 1975.He received the Ph.D.degree from Huazhong University of Science and Technology in 2006.Currently，he works in Shanghai Bell Co.，Ltd.as a system advisory engineer.His research concernsMIMO related technologies，such as space-time coding and multi-user detection.

Email：Bijun.a.zhang＠alcatel-sbell.com.cn

張碧軍（1975—），男，四川巴中人，2006年于華中科技大學(xué)獲博士畢業(yè)，目前在上海貝爾股份有限公司從事TD-LTE產(chǎn)品系統(tǒng)設(shè)計(jì)相關(guān)工作，主要研究方向?yàn)榭諘r(shí)編碼、多用戶檢測(cè)等MIMO相關(guān)技術(shù)；

LIYa-lin was born in Fuyang，Anhui Province，in 1981.He received the Ph.D.degree from University of Science and Technology of China in 2008.He has been working in Shanghai Bell Co.，Ltd.as a post-doctor and wireless system advisory engineer since 2008.His research concernsmulti-antenna signal processing and the design ofmulti-antenna transceiver in LTE system.

Email：Yalin.a.li＠alcatel-sbell.com.cn

李亞麟（1981—），男，安徽阜陽(yáng)人，2008年于中國(guó)科學(xué)技術(shù)大學(xué)獲通信與信息系統(tǒng)專業(yè)博士學(xué)位，2008年至今在上海貝爾股份有限公司分別作為博士后和無(wú)線系統(tǒng)主任工程師工作，主要研究方向?yàn)槎嗵炀€信號(hào)處理、多天線收發(fā)機(jī)設(shè)計(jì)；

WANGWei was born in Jiangxi Province，in 1975.He received the Ph.D.degree from Beijing University of Posts and Telecommunications in 2006.He is now working in Shanghai Bell Co.，Ltd.as a system advisory engineer in Wireless R＆D Department.His research concerns algorithm design and simulation formobile communication base-station systems.

Email：Wei.si.wang＠alcatel-sbell.com.cn

王偉（1975—），男，江西人，2006年于北京郵電大學(xué)獲通信與信息系統(tǒng)專業(yè)博士學(xué)位，現(xiàn)為上海貝爾股份有限公司無(wú)線產(chǎn)品部系統(tǒng)設(shè)計(jì)主任工程師，主要研究方向?yàn)橐苿?dòng)通信基站系統(tǒng)的算法設(shè)計(jì)與仿真；

JIANG Zhi-ningwas born in Hunan Province，in 1976.He received the M.S.degree from University of Science and Technology of China in 2000.He is now working for ShanghaiBell Co.，Ltd.as a system consultant engineer in Wireless R＆D Department.His research concerns algorithm design and simulation ofmobile communication base-station systems.

Email：Zhining.jiang＠alcatel-sbell.com.cn

蔣智寧（1976—），男，湖南人，2000年于中國(guó)科技大學(xué)獲通信與信息系統(tǒng)專業(yè)碩士學(xué)位，現(xiàn)為上海貝爾股份有限公司無(wú)線產(chǎn)品部系統(tǒng)設(shè)計(jì)顧問工程師，主要研究方向?yàn)橐苿?dòng)通信基站系統(tǒng)的算法設(shè)計(jì)與仿真；

LIN Ling-fengwas born in Fujian Province，in 1976.He received the M.S.degree from University of Science and Technology of China in 2000.He is now working for ShanghaiBell Co.，Ltd.as a system consultant engineer inWireless R＆D Department.His research concernswireless system design.

Email：Lingfeng.lin＠alcatel-sbell.com.cn

林凌峰（1976—），男，福建人，2000年于中國(guó)科技大學(xué)獲通信與信息系統(tǒng)專業(yè)碩士學(xué)位，現(xiàn)為上海貝爾股份有限公司無(wú)線產(chǎn)品部系統(tǒng)設(shè)計(jì)顧問工程師，主要研究方向?yàn)橐苿?dòng)通信基站系統(tǒng)設(shè)計(jì)。

An Efficient Scheme for Single-cell Point-to-multipoint e-MBMS Transm ission?

ZHANG Bi-jun??，LIYa-lin，WANGWei，JIANG Zhi-ning，LIN Ling-feng
（WSPDWireless R＆D Department，Alcatel-Lucent Shanghai Bell Co.，Ltd.，Shanghai201206，China）

Multimedia broadcast/multicast service（MBMS）is one typical service defined in 3GPPRelease 6.In Long Term Evolution（LTE），evolved（e）-MBMShas also been defined to enhance the MBMS transmission.In this paper，an efficient scheme applicable to single-cell point-to-multipointe-MBMS transmission is proposed.It can be seemed as the combinations of downlink transmit diversity，Direction of Arrival（DoA）based beam-forming and hybrid-ARQ（HARQ）retransmission.Simulation results show the significant performance improvement compared with pure downlink transmit diversity scheme.

e-MBMS；LTE；beam-forming；DoA；transmit diversity；HARQ

TN911；TN919.8

A

1001－893X（2013）02－0117－05

10.3969/j.issn.1001－893x.2013.02.001

?Received date：2012－08－01；Revised date：2012－09－18

2012－08－01；修回日期：2012－09－18 Foundation Item：The National Science and Technology Major Project（2012ZX03001010）

國(guó)家重大專項(xiàng)（2012ZX03001010）

??Corresponding author：Bijun.a.zhang＠alcatel-sbell.com.cn通訊作者：Bijun.a.zhang＠alcatel-sbell.com.cn