Uniform design simulated annealing for optimal access point ...

The 14IhIEEE 2003 International Symposium on Persona1,lndoor and Mobile Radio Communication Proceedings

Uniform Design Simulated Annealing for Optimal Access Point Placement of High Data Rate Indoor Wireless LAN Using OFDM Tao Jiang Ikpairnient o f Electronics & Infoi-mation Engineering. Huiirhong University o f Science & Technology, Wuhan, China hust-itao@ 1 6 ~ . c o m

Guangxi Z l i u Department o f Electronics & Information Engineering. Huazhong University o f Science & Technology, Wuhan, China g$huOmail,hust,edu.cn

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paper investigates the optimal access point (AP) in simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for high data rate indoor wireless LAN. We aim t o determine the best combination o f multiple AP placements that minimizes average bit e r r o r r a t e (BER) of terminals when in put information including an indoor configuration. a number APs, and total transmission power i s gken a priori. Since OAPP i s categorized as a hard combinatorial problem with many variables and constraints. w e applied a nonlinear optimization scheme called uniform design simulated annealing (UDSA) t o search f o r an approximate optimal solution and analyzed i t s performance in derail. The simulation results demonstrate that the UDSA algorithm has been successfully applied to OAPP and i t s rl'fcfectivenrsa was also confirmed i n comparison with rery fast simulated annealing (VFSA) and local search (LS) algorithms. placement (OAPP)

I.

IN711UDIICI ION

.I'his paper investigates an optin~al access point (AP) placeiiienr (OAPP) iii simultaneous broadcast system using orrliogoiial frequency division multiplexing (OFDM) for highspeed indoor wireless L A N in EHF band. In our OAPP prubleni. we aim to determine the best combination of inultiple AP placeinents that iniiiiniizes average bit error rate (BER) o f all teniiitials when input information including an indoor layout with terminals' and partitions' height and locations. a number of APs. and total traiisinissioti power ale given a priori. We assume that multiple APs installed 011 a ceiling simultaneously transmit identical information using identical frequency in dniwilink while a terminal simply sums up all the signals in order of arriving without usin:: either co-phase logic nor s\vitching logic [ I ] [2]. Taking accoimt o f static obstructions a n d iiot dynamic reflectors such as inoving people in a given indoor layout. an optimal placement of multiple APs is supposed to be determined in a site-specific manner. It inust be of'a great interest to introduce an OAPP inethod applicable to viiriuus indoor configurations as well as to wide range of EHF Imids accoi-ding to uset-s' requireinents. In our OAPP problem. we calculate BER at each terminal

location by iiirans o f ray tracing. which considers propagation path loss. reflection due to walls and partitions, and

transmission through partitions [2-2]. In the calculation o transmission coefficient and reflection coefficient. we need tr apply a discrete expression according to the relative position, o f APs, terminals and obstructions. The transinissiol coefficient i s formulated as a discontinuous function dependin? on whether an obstruction i s inside a traced ray or not Regarding the reflection c.oefficient. we should test if a trace< ray meets a wall or othei- obstructions. As a result. analytica approach may not be applicable for the OAPP problem becausi the cost function in terms o f average BER includes : discontinuous variable. Furthermore, since many variables ani complicated constraints are involved. this problem i. categorized as a hard combinatorial problem where exac search for the best solution is practically impossible due to a, exponentially growing calculation time. Then. we applied i nonlinear optimization scheme called uniform design ant simulated annealing (UDSA) which consists of globa optimization and occasional long jumps. Uniform design i s : good method for the problem of many control factors and higi accuracy. A t each iteration, we apply uniform design !I arranging APs and simulated annealing to modifying these AI? while simulated annealing generates a new state from Cauchy like distribution which is a function o f a control parametc called temperattire and then decides whether to accept or rejec it. This scheme allows for searches far beyond the curren position at high temperatures, while at low temperatures i looks for improvement in the close vicinity o f the curren model. Thus, UDSA is considered efficient to guarantee i statistically optimal solution with reasonable coniputationa effort. The paper is organized as followiny. In section II. w i present the problem as well as the simultaneous broadca: system using OFDM. Section 111 describes the method o uniform design and discourse the principe of UDSA algorithli and its application to the OAPP problem. After the simulatiol results in section IV, the conclusion is given in section V.

II.

ACCESS POINT P L A C E M E N T PROBLEM

OFDM i s considered as an effective multicarrii transmission technique against multipath fading in radi, communications systems. The principle o f this technique i:

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The;l4~lEEE.PUOSiMmational:Symposlum on Persona1,lndoor and Mobile Radio Communication Proceedings

iluniiiiitriiiy [lie data in par$l,yl ,is,iiig.. Insa?~,subcarriers operaiiiig at IOU'data rare: By insei.riiig a guaid interval::that is ihnger ihiin the inaxiiiitini dela? spread o f arriving paths. we caii y a i - a i i t e e complete eliiniiiation of ISI. which inakes high data triinsiiiission possible 141. using this feature. nlultiple APs in ii single cell can rransm entical information u$ng an ideiiiicnl li-equency band. while,a teriiiinai can simply sum up :ill tlir signals in order ofarriving without using either c logic or switching logic. l i i the OAPI' probleiii. we" aim at-'le~~riiitning'.,the best coiiihiiiaiion of iniiiltiple AP placements that iniiiiinizes average B E K d terminals based on input iiiforinarion ainong a large iiunibcr o l discrete feasible solutions. The input information iiiciudei the following: ( I ) indoor layout:.including rooiii. size. Iocaiioiis and heights o f trriniiial anierliia tiixerial ofwalls: (21 the iiuinher of APs: WK (4'1 grid size: (51 design pwaineters'.&ch'& antenna i i i i i iirrqueiic?. band 121. In indoor environiiieiii model, We w i w that all teriiiiiials are tixed and'thit APs'are.installed at criling l w e l as shown iii Fig.1. . .,: ,;, .. , I

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lii tlir calculatioii ofthe BEReteach terminal in a given AP ray tracins based on iinaging theory is applied to

111 OAPP probl&i, the cost function (3) is to ininiinize the average BER of N,terminals. Coiistrainrs from ( 5 ) to (9) ensure that N,,,, At's. N, terminals and /Vi, partitions are locared within a room. Transinksion power per A P is iiniforiiily distributed as expressed in (8). The ( 9 ) shows tliat total transinission coefficient of each path can get from the product o f transmission coefficient due to a11 partitions.

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prrdict the received power. Ray .tracing is:-.considesed.as a p o w c s f ~ i ltool for site-specitic prediction.in :EHF hands. wliere tlic \vawleiigtli i s iniicli slioiier an ,!lie size of the e i i ~ ~ i r ~ i i i i i i e iIni t . our model. we ta account, of path loss, rrtleciioii diie IO wal1.s and paititions.'and transinission through partitions. Since transiiiissioii'throii' is srilall. liere we assiiine the transmi ohsirucrion is inside a traced ray.'W rrrlecrioii iiot only iu reduce ,conlp . ? w i t ! the iiitlueiice or' reflected p hea\'il) depends oil a sire-specific indoor coiitigiiration [ I I . U.

1 Grid size ____ -. Numberofqridr onx-.r;- axis Anrcima giiiii o f A P . leriiiiiial ._ 'i'of81 fiunsmi\sion cocfficirm of)-11, i c r n i i n u l ~I-ih ~ patli I ___

The DER in OFDM-DQPSK inodulation in simultaneous broadcast system is introduced below. Froin D,(s), the power o f desired signal of i-th teriiiiiial at each subcarrier in a giveii set o f A P locations s. and the Gaussian noise power N. we can detine the BER of;-th terminal in a giveii set o f A P location s .nored p&). The innxiiiiiiiii number o f paths L generated by an A P installed is nine. coinposed by one direct path, four onebounce reflected paths from walls. and those from partitions assuming four reflected paths occur by surrounding partitions.

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I I I d e r to forinuliitr the OAI'P problem, the following iiecisim variables are introduced [I-21. ' . . .": , :'

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The 141h IEEE 2003 International Symposium on Persona1,lndoor and Mobile Radio Communication Proceedings

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