PERFORMANCE ANALYSIS OF NONDIRECTED IR WIRELESS CHANNEL IN INDOOR ENVIRONMENT USING STATISTICAL DISTRIBUTION.. Abstract: PRAKASH PATIL Priyadarshini College of Engineering, Nagpur, RTM S University of Nagpur, Maharashtra, India. Phpatil2005@yahoo.co.in. DILIP SHAH. Principal, G. H. Raisoni College of Engineering and Management, Pune, Maharashtra, India. Dilip.d.shah@gmail.com SHRIKANT BODHE Principal, College of Engineering, Pandharpur, Maharashtra, India. Director, Bosh Technologies, Pune, India. skbodhe@gmail.com The future short range wireless communication in an indoor environment jncludes the nondirected Infrared (IR) Wireless communication. It is essential since there is a tremendous growth of bigger residential and commercial complexes. Also, nowadays use of portable devices such as LAPTOP, PDA etc. has been increased and the connectivity to such devices is the must without any interruption. In indoor environment both the transmitter and receiver are located inside the room. An empty rectangular is considered for the simulation purpose. The major interest in this simulation deals with the diffuse configuration (Non-directed Non-LOS) of the transmitter and the receiver. The IR wireless channel modeling is performed with multipath IR signals transmitted by the IR Transmitter and received by the receiver after multiple reflections from the reflecting surfaces such as ceiling, floor walls etc.impulse response is the fundamental predictor of IR channel modeling and it is characterized by using Monte Carlo simulation.this paper estimates the mean received power and variance for different statistical distributions such as Rician, Gamma and Nakagami derived from histograms curve fitting for various receiver heights and radii. in time domain approach. Keywords: Short Range Wireless Communication; Infrared (IR) ;Impulse Response, statistical distribution. Time domain 1. Introduction The materialization of portable information terminals in indoor environments is accelerating the opportunity of wireless digital links and local-area networks (LANs). The Portable devices should have access to all of the services that are available on high-speed wired networks. Unlike their wired counterparts, portable devices are subject to severe restrictions on power consumption, size and weight. The desire for inexpensive, high-speed links satisfying these requirements has motivated recent interest in infrared wireless communication [1]-[2]. The main advantages of the IR technology are the provision of an enormous unregulated bandwidth and the absence of interference generated communication users placed on adjacent rooms. In spite of optical wireless communication is attractive for certain high-speed applications, there are several aspects which impair its performance. One of the most important aspects is the intersymbol interference (ISI) due to multipath dispersion ISSN : 0975-5462 Vol. 4 No.05 May 2012 2270
[3]. The other important impairment for indoor infrared communication systems results from the strong interference induced by ambient light such as natural and man-made (artificial) light. The multipath propagation causes a spread of the transmitted pulse, which results in ISI [4]. This degrades the performance of non-directed indoor IR wireless communication system 2. IR Link Design. Indoor infrared wireless communication can employ various designs, and it is convenient to classify them according to two criteria. This classification of IR link is shown in Fig.1 [5] Fig. 1.Classification of IR Link.[4]. The first classification refers to the directionality of the transmitter and receiver. Directed links employ directional transmitters and receivers, which must be aimed in order to set up a link. Non- directed IR links employ wide-angle transmitters and receivers, alleviating the necessitate for pointing. Directed IR link design provides maximum power efficiency due to reduced path loss and reception of ambient noise. Conversely, non directed links may be more suitable to use, mostly for mobile terminals, since they do not require aiming to the transmitter or receiver. In case of hybrid link both transmitters and receivers are combined with different degrees of directionality. The second classification refers to whether the link relies upon the survival of an uninterrupted LOS path between the transmitter and receiver. LOS IR links rely upon such a path, while non-los relies upon reflected paths of the light from the ceiling, walls or some other diffusely reflecting surface within a specific room. LOS link design offers maximum power efficiently and reduces the multi-path distortion. Non-LOS IR link design increases link stability and simplicity of use, allowing the link to operate even in presence of obstacles between the transmitter and receiver. Non -directed non-los link design provides the utmost stability and simplicity of use which is often referred to as diffuse link.[6]. The complete block schematic of nondirected IR wireless communication system in indoor environment is given below. ISSN : 0975-5462 Vol. 4 No.05 May 2012 2271
Figure 2: Block Diagram of indoor infrared wireless channel In the figure given below infrared Led is used as the transmitter which converts the input signal into corresponding infrared signal. It is further transmitted via free space medium. On the receiver side APD is used as the photodetector that converts the infrared signal into the corresponding photocurrent 3. Impulse response estimation The equivalent baseband model of non-directed infrared wireless link can be summarized by the relation given below, h t +Nt Y t =R X t (1) Where, indicates the convolution R is the photo detector responsively (in A/W), and h (t) is the channel impulse ambient light, can be modeled as white Gaussian noise [7].It cannot be negative and must satisfy eye safety regulations [7], and is given by, The input signal X (t) is the instantaneous optical power of the transmitter. The output signals Y (t) is the instantaneous photo current delivered by the photodetector. It is the product of the photo detector responsivity (sensitivity) R in A/W and the integral over the surface of the photo detector of the instantaneous IR power at every location the signal propagates between the transmitter and the receiver through a room via probable reflections. The IR channel can be modeled as a baseband linear system characterized by the input power X (t), the output current Y (t), the additive white Gaussian noise N (t) and an impulse response h (t) as shown in figure 2.Different temporal or frequential impulse responses are considered as fixed for a specific physical configuration of transmitter, receiver and reflective surfaces in indoor environment. [6].With the movement of the transmitter, the receiver or the objects in the room, the impulse responses get changed. The impulse response is quasistatic because of high signaling rates, high order diversity of the large area receiver. In many applications, it is assumed that IR links are operated in the presence of intense infrared and visible background light that results in additive white nearly Gaussian noise N(t) which is the limiting factor in the signal to noise ratio (SNR) of a well designed receiver. The channel model is characterized by two parameters, rms delay spread D rms and optical path loss H (0) which cause Intersymbol interference (ISI) and signal attenuation, respectively. The impulse response of an infrared wireless link can be represented as 6 6a ht () H(0) ut () 7 ( t a) Where, (2) ISSN : 0975-5462 Vol. 4 No.05 May 2012 2272
ut () =is the unit step function., The value of a depends upon the room dimension and locations of the transmitter and the receiver. If both transmitter and receiver are co-located then we have, a 2 H / c (3) Where, H = Height of the ceiling Intensity modulation with direct detection (IM/DD) is the only feasible method of communication due to cost and complexity. [6]. The transmitted optical power of the source X(t) is directly varied by changing the drive current according to the modulating signal. The receiver uses the photodetector wherein the photocurrent Y(t) is directly proportional to instantaneous power incident upon it. It means it is proportional to the square of the received electric field. 3.1 Algorithm and its implementation The impulse response for line-of-sight (LOS) path is given by the relation 0 n h t; T; R 1 n cos c d rect / FOV t d /, 2 (4) Similarly, the impulse response for the higher order reflections (i.e. q 0 ) is calculated recursively. with the help of an algorithm. From the equation (8), we can write: h t; T r, q t; T; R0 h n, / 2, S da h q1 t ; r, n, 1, R i n cos 2 d cos hence h h q t is described as follows. n N n i h i cos cos i 2 i1 S q N 0 t T, R t; T, t;, R : 1 R (5) 1 i q1 rect 2 / 2 h t R / C ; r, n,1, R A (6) ISSN : 0975-5462 Vol. 4 No.05 May 2012 2273
4. Simulation of Non- directed IR channel. The simulation parameters required to perform the simulation are listed in the Table 1.shown below. Table 1. Simulation parameters: Parameter/configuration Rom Dimension Reflectivity ( ) Transmitter (T x ) Receiver (R x ) Length(X) Width Y) Height (Z) Wall Ceiling, Floor Mode X Y Z Area FOV X Y Z Room Environment 6 4 3 0.6 0.6 0.6 1 3 2 3 1 70 3 2 Var 4.1 Simulation set up inside the room This is totally novel system for the simulation analysis if nondirected indoor IR channel. We consider an empty rectangular room where the transmitter, receiver and the reflecting surfaces such as ceiling and floor are positioned. To characterize the impulse response of nondirected IR channel using intensity modulation direct detection (IM/DD) in indoor environment, we have used the Monte-Carlo simulation The simulation parameter details are as follows 1. Empty rectangular room with dimensions: (6,4,3) 2. Transmitter Position: Ceiling center. 3. Transmitter radiation pattern mode: Mode 1 4. Receiver Position: At a height of 1m and 2 m from floor and at the center of floor initially. 5. Variable Receiver height : 1m, 2m and 3m 6. Receiver is revolved around the transmitter with different radii varying from 1m to 2m in steps of 0.25 5. Simulation Results and discussion: For the performance analysis of non-directed IR channel distribution plots from the histograms are obtained and those are listed in Fig. 3 as follows: ISSN : 0975-5462 Vol. 4 No.05 May 2012 2274
(a)rx Ht 1m and Rx Rad. 1m (b) Rx Ht 1m and Rx Rad. 1.5m ( c) Rx Ht 1m and Rx Rad.2m (d) Rx Ht 2m and Rx Rad. 1m (e) Rx Ht2m and Rx Rad. 1.5m (f) Rx Ht 1m and Rx Rad.21m ISSN : 0975-5462 Vol. 4 No.05 May 2012 2275
(g) Rx Ht 3m and Rx Rad. 1m (h) Rx Ht 1m and Rx Rad. 1.5m (i) Rx Ht 1m and Rx Rad. 2m. Fig 3 : Distribution fit for Rician, Gamma and Nakagami distribution with Rx Ht1m, 2m and 3m For Rx radius varying from 1m to 3m in steps of 0.25 m. From all the above plots we have analyzed the data which provides the mean received power and variance for different combinations of receiver heights and radii. Curve fitting gives all the above histograms are tested for the distributions such as Rician, Gamma and Nakagami. It is required to analyze the best possible fit of the histograms. Here we have considered upto third order reflections. Table 2 illustrates the statistical values of mean received power distribution and variance at different geometries of the transmitter, receiver and reflecting surfaces inside an empty rectangular room. ISSN : 0975-5462 Vol. 4 No.05 May 2012 2276
Table 2: Mean and Variance for different distributions Experiment for Rx Parameters Rx Rad.=1m Rx Rad.=1.25m Rx Rad.=1.5m Rx ad.=1.75m Rx Rad.=2m Rx Rad.=1m Rx Rad.=1.25m Rx Rad.=1.5m Rx Rad.=1.75m Rx Rad.=2m Rx Rad.=1m Rx Rad.=1.25m Rx Rad.=1.5m Rx Rad.=1.75m Rx Rad.=2m Rician Gamma Nakagami Mean Variance Mean Variance Mean Variance 32.622 0.862 32.626 0.86 32.62 0.864 32.637 0.917 32.637 0.916 32.637 0.916 32.555 0.844 32.555 0.848 32.555 0.846 32,557 0.852 32.557 0.856 32.553 0.854 32.482 0.865 32.482 0.866 32.482 0.865 34.494 0.820 34.494 0.822 34.494 0.822 34.40 0.848 34.40 0.851 34.40 0.849 34.326 0.939 34.326 0.940 34.326 0.939 34.277 0.923 34.277 0.925 34.277 0.923 34,238 0.921 34,238 0.922 34,238 0.921 34.478 0.846 34.478 0.850 34.478 0.848 36.432 0.900 36.432 0.902 36.432 0.901 36.329 0.930 36.329 0.933 36.329 0.931 36.220 0.959 36.220 0.962 36.220 0.960 36.153 1.004 36.153 1.007 36.153 1.005 6. Conclusion: From the above given results it has been observed that the Rician distribution is the best fit for the performance analysis of non-directed IR wireless communication in an indoor environment. The research further reveals that the IR channel can be modeled using the Rician distribution. From this outcome of the research we can suggest the received power distribution at certain fixed geometry of the transmitter and receiver in an empty rectangular room. This is the innovative approach of modeling the non-directed IR channel in the multipath Indoor environment for the high speed secured communication with unlimited bandwidth providing the fruitful communication amongst various portable devices located inside the room. References: [1] Gfeller F. R. and Bapst U. H., (1979):Wireless In-House Data Communication via Diffuse Infrared Radiation, Proceedings of the IEEE, Vol. 67, No. 11, pp. 1474-1486. [2] Infrared Data Association standards can be obtained at the organization s home page on the : World Wide Web: http://irda.org [3] Lomba C. R. (1997. ): Infrared Wireless Indoor Communications: modeling, Simulation and Optimisation of the Optical Channel, PhD thesis, Dept. of Electronics and Telecommunications, University of Aveiro, Aveiro, Portugal, [4] António M. R.,Tavares, Rui J.,Valadas M. T., et al, :Performance of wireless infrared transmission systems considering both ambient light interference and inter-symbol interference due to multipath dispersion, SPIE s Symposium on Voice Video and Data Communications Conference on Optical Wireless Communications Boston, MA, USA, 1-5 November 1998 [5] Padgett J.E., C. G. G., (1995), :Overview of wireless personal communication, IEEE communication Magazine, vol.33, no.1, pp. 28-41, ISSN : 0975-5462 Vol. 4 No.05 May 2012 2277
[6] Kahn Joseph M. and Barry John R. (1997), : Wireless infrared communication, Proceeeding of IEEE, vol. 85, PP. 265-298, [7] Barry J. R., (1994.): Wireless Infrared Communications, Kluwer Academic Publishers, Norwell, Mass, USA, [8] Barry J. R., Kahn Joseph M., Krause and et al G. Messerschmitt, (1993) :Simulation of Multipath Impulse response for Indoor Wireless Optical Channels. IEEE Journal on selected areas in Communication vol. 11 No.3, pp. 367-379. ISSN : 0975-5462 Vol. 4 No.05 May 2012 2278