C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....signals at the receiver introduced by the deterministic path attenuation, shadowing and multipath fading. Due to the capture effect, a frame with the strongest received signal strength can be correctly decoded at the receiver even in the presence of simultaneous transmission of multiple stations [1, 2]. Capture effect is feasible in an indoor environment consisting of low power transmitting stations, e.g. a Wireless LAN [3, 4] In this paper, we study the influence of capture effect over the IEEE 802.11b Distributed Coordination Function (DCF) 5] in presence of near far effect and or Rayleigh ....

C.T.Lau and C.Leung, Capture Models for Mobile Packet Radio Networks, IEEE Trans. on Commun., Vol. COM-40, pp. 917-925, May 1992.

.... First, a deterministic dependence of the received power on the distance between the transmitter and receiver, r, is considered: the average power is proportional to a function g(r) Ar , with the propagation exponent, We assume a bell shaped trac distribution around the common receiver [4][14] which corresponds to a probability density function (pdf) for the distance of a random point from the receiver: f(r) 2re r 4 =4 ; r 0: 1) We prefer the bell shape over the uniform spatial distribution because the latter ignores the fact that retransmissions arrive predominantly ....

.... not allowed to be arbitrarily close to the base station, then indeed lim n 1 Pn = 0 [17] 19] Neither the bell shaped, nor the uniform spatial distribution satis es this requirement, and the so called punctured distributions where f(r) 0 for r 2 [0; are considered to alleviate the quandary [4][17] However, punctured bell shape yields almost identical capture probabilities for all 2 [0; 0:1] and hence we can safely employ the model in equation (1) which corresponds to = 0 [17] C. Antenna Diversity Antenna diversity, where two (or more) antennas separated by at least half ....

C. T. Lau and C. Leung, \Capture models for mobile packet radio networks", IEEE Transactions on Communications, vol. 40, pp. 917-925, May 1992.

....and exposed (b) terminal problems. The dotted circles indicate the radio transmission ranges. C D A B E F Figure 2. Illustration of packet loss due to interference. ceived powers are above the prescribed threshold, if the signal power of one of the packets sufficiently exceeds the others [10]. Due to these reasons, a pre defined fixed threshold for evaluating the channel busy idle status is highly inadequate to predict the probabiltiy of success of a transmitted packet in wireless. It would be beneficial to utilize the level of interference for a better prediction. 4 Multichannel ....

C. T. Lau and C. Leung. Capture models for mobile packet radio networks. IEEE Transactions in Communications, 40(5):917--925, 1992.

....transmitters, is able to receive a packet when the received signal power level is not lower than the threshold G=S b DW [dB] 4) where S b is the global average received signal power at the distance of 0.5 length units from an access port. Capture model: The terminals utilize power capture [8]. In the event of colliding packets, the packet with the strongest signal is captured, if the SIR is above the capture ratio g, where g 1. That is, a terminal may capture a transmission from access port i if S S i j j i g (5) where S j is the received signal power from access port j. III. ....

Lau, C. T., Leung, C., "Capture Models for Mobile Packet Radio Networks", IEEE Trans. COM-40, No. 5, pp. 917-925, May 1992.

....number of successful receptions when n packets collide, Cn , and their limit as n 1, C1 , are evaluated according to this model; some theoretical developments about C1 are proposed. Also, of some interest is the sensitivity analysis of the performance to the system parameters; as already known [5, 9, 12], the outage threshold (capture ratio) has a significant impact on the performance, whereas the influence of the shadowing parameter, oe, vanishes as the collision size increases, since C1 does not depend on oe [5] The dependence on the fading model, and in particular on the Rice factor, K , is ....

....on the coding strategy adopted and on the modulation scheme used. Note that the presence of the factor n in (3) is due to the fact that all contending users are potentially useful , and that they are all identically distributed. These probabilities can be analytically evaluated in some instances [5, 12], whereas in general they can be computed only by simulation. 4 Double diversity Due to the multiple reception capability, more than a single packet may be correctly decoded in one slot, and therefore the derivation of the capture probabilities is not as simple as in the previous section. In ....

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C.T. Lau and C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. Comm., vol. COM-40, pp. 917-925, May 1992.

....rich bibliography therein) and can be regarded as an approximation in the presence of coding. Although some more accurate models are under study, we chose to adopt this model for its simplicity and because it is consistent with most of the literature, allowing direct comparisons. Lau and Leung [10] have introduced a model that uses a probabilistic function of the signal to interference ratio, as opposed to a strict threshold function, to model the type of modulation and coding used. While such an approach could be pursued here, it introduces yet another integral expression into an already ....

....considered as a practical example of application of the above theory. A number of challenging research problems related to this work remain unsolved. These problems include the study of a more precise capture model that includes aspects of the modulation and coding scheme (e.g. see Lau and Leung [10]) development of an exact analytic expression for C1 , considering cases of higher diversity order (i.e. greater than two as considered in this paper) and the analytic treatment of correlated Rician fading and of the maximal ratio combining strategy. APPENDIX A: MARCUM S Q FUNCTION AND ....

C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Trans. Commun., vol. 40, pp. 917-- 925, May 1992.

.... [4] in particular, have been considered attractive because of their intrinsic ability of exploiting capture [5, 6, 7] Capture is the capability that receivers have to detect a signal in the presence of other signals, provided that the signal to interference ratio exceeds the capture threshold [8]. In the cellular environment, received signal levels are strongly influenced by the near far effect and the fading phenomenon, which make the signal levels randomly vary [9, 10] Thus capture becomes a probabilistic phenomenon, whose failure is naturally handled by retransmission techniques. In ....

C.T. Lau and C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. Comm., vol. COM-40, pp. 917-925, May 1992.

....parallelism occurs when the transmission in one cell can be successfully detected because the power of transmissions in other cells, called interference, is sufficiently small. The ability of the receiver to detect a signal in the presence of interference noise is known as capture effect [1, 3], and the signal to noise threshold needed to allow capture is denoted as capture ratio. With the usual values of the capture ratio for narrowband systems, concurrent transmissions in adjacent cells can not be tolerated. The solution to this problem can be obtained either by decreasing the ....

C.T. Lau, C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. Comm., vol. COM-40, pp. 917-925, May 1992.

....any specific distribution for the fi i s (except for the fact that they are i.i.d. so that we are keeping ourselves as general as possible. In particular, in this model fading and shadowing do not need to be Ricean and log normal, respectively. Based on an approach similar to the one in [15], it is possible to show the following result, stated here without proof [16] Theorem: For a bell shape distribution of traffic and j = 4, if E[fi 3=2 i ] 1, then C1 = lim n 1 (n 1)P fl 0 P n i=1 fl i b = 2 p b ; 12) regardless of the actual distribution of the fi i s. We ....

C.T. Lauand C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. on Comm., vol. COM-40, pp. 917-925, May 1992.

....scheme used. The factor n is due to the fact that all contending users are potentially useful, and that they are all identically distributed. This probability can be analytically evaluated in the case of Rayleigh fading [13] and in the absence of fading for the bell shape traffic model [21]. In general, the computation can be efficiently performed via Monte Carlo simulation. III. NUMERICAL RESULTS In Fig. 1, the capture probabilities, Cn , are plotted vs. the collision size, n, for some values of b and for both uniform and bell shape traffic distribution. Note the strong ....

....the presence of shadowing corresponds to superior performance and weaker dependence on the fading model. As discussed in [13; 15; 21] the mobile users should not be allowed to be arbitrarily close to the base station. As an example, we consider a punctured uniform (bell shape) distribution [21], where the users are uniformly (bell shape) distributed except for a circle of radius , centered in the common receiver. Fig. 3 shows the performance of such a system, for oe = 6 dB, b = 6 dB and various values of . A comparison with Fig. 1 shows that the curves for = 0:01 practically coincide ....

[Article contains additional citation context not shown here]

C.T. Lau, C. Leung, "Capture models for mobile packet radio networks," IEEE Trans. on Comm., vol. COM-40, pp. 917-925, May 1992.

....effect. In particular, the use of classic Slotted ALOHA [1, 2, 3] in the mobile radio environment has been studied [4, 5, 6, 7] The conditional throughput Cn , i.e. the average number of packets which are correctly received per slot, given the number of colliding packets, n, has been computed [8, 9, 10, 11, 12, 13]. Some research has also been devoted to the closed form computation of C1 = lim n 1 Cn , which is a good approximation of Cn for large n and is related to the stability of the system without retransmission control [11, 14, 15] Unlike in the case of a single receiver, for which C1 has been ....

C.T. Lau, C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. on Comm., vol. COM-40, pp. 917-925, May 1992.

....In this situation, power capture can occur when differences in received power levels result in the successful reception of a packet in the presence of, typically weaker, contending transmissions. The power capture effect has a significant impact on the throughput of random access protocols [1, 2, 3, 4]. In a mobile radio system, the power of the signals received from the different transmitters will vary due to differences in the length of the transmission path and due to multipath fading effects. These physicallyinduced power variations have been observed to enhance the power capture effect and ....

C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Trans. Commun., vol. 40, pp. 917--925, May 1992.

.... [4] in particular, have been considered attractive because of their intrinsic ability of exploiting capture [5, 6, 7] Capture is the capability that receivers have to detect a signal in the presence of other signals, provided that the signal to interference ratio exceeds the capture threshold [8]. In the cellular environment, received signal levels are strongly influenced by the near far effect and the fading phenomenon, which make the signal levels randomly vary [9, 10] Thus capture becomes a probabilistic phenomenon, whose failure is naturally handled by retransmission techniques. In ....

C.T. Lau and C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. Comm., vol. COM-40, pp. 917-925,May 1992.

....number of successful receptions when n packets collide, Cn , and their limit as n 1, C1 , are evaluated according to this model; some theoretical developments about C1 are proposed. Also, of some interest is the sensitivity analysis of the performance to the system parameters; as already known [5, 9, 12], the outage threshold (capture ratio) has a significant impact on the performance, whereas the influence of the shadowing parameter, oe, vanishes as the collision size increases, since C1 does not depend on oe [5] The dependence on the fading model, and in particular on the Rice factor, K , ....

....on the coding strategy adopted and on the modulation scheme used. Note that the presence of the factor n in (3) is due to the fact that all contending users are potentially useful , and that they are all identically distributed. These probabilities can be analytically evaluated in some instances [5, 12], whereas in general they can be computed only by simulation. 4 Double diversity Due to the multiple reception capability, more than a single packet may be correctly decoded in one slot, and therefore the derivation of the capture probabilities is not as simple as in the previous section. In this ....

[Article contains additional citation context not shown here]

C.T. Lau and C. Leung, "Capture models for mobile packet radio networks", IEEE Trans. Comm., vol. COM-40, pp. 917-925, May 1992.

....signalling can overcome the propagation effects to enable reliable communications. A medium access control (MAC) protocol is used by a WLAN to enable multiple WTs to efficiently share the same wireless channel [2] Performance of contention based MAC protocols can be enhanced by the capture effect [3][4] at the receiver which enables it to correctly receive one of several colliding packets, based on different signal strengths of the packets arriving at the receiver, or special property of the signaling technique. We investigate the performance of infrastructure WLANs employing a novel ....

C. T. Lau and C. Leung, "Capture Models for Mobile Packet Radio Networks", IEEE Transactions on Communications, vol. 40, pp. 917-925, May 1992.

....destroyed, so that multiaccess interference severely limits the throughput efficiency of the channel. However, the capture effect enables one of several colliding frames to capture the receiver and be correctly received. This is possible due to the power differences between the interfering signals [10], or the use of DS SS signaling [11] Therefore the capture effect greatly increases the throughput efficiency of the channel in the presence of multiaccess interference. The performance of multi receiver slotted Aloha access, taking into account of the capture effects, has been analyzed [12] ....

.... slotted Aloha access, taking into account of the capture effects, has been analyzed [12] However, this analysis unrealistically assumed that each frame is received with equal power at all the receivers, and the capture effect is based only on power differences of the received signals [10]. We present a more accurate model for DS SS signal capture, where the frame error rate of the signal successfully captured by the code synchronizer in a receiver is explicitly evaluated with respect to the effects of multipath and multiaccess interferences. We present simulation results for ....

C. Lau and C. Leung, Capture models for mobile packet radio networks, IEEETrans.Commun. 40 (1992) 917925.

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C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992.

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C. T. Lau and C. Leung. Capture models for mobile packet radio networks. IEEE Trans. on Communications, 40(5):917--925, May 1992.

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C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992.

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C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992. 153

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C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992.

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C. Leung and C. T. Lau, "Capture models for mobile packet radio networks," IEEE Trans. Commun., vol. 40, pp. 917--925, May 1992.

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C. T. Lau and C. Leung, "Capture models for mobile packet radio networks," IEEE Transactions on Communications, vol. 40, no. 5, pp. 917--925, May 1992.

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C. T. Lau and C. Leung. Capture models for mobile packet radio networks. IEEE Transactions on Communications, 40(5):917--925, 1992.

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C. Lau and C. Leung. Capture models for mobile packet radio networks. IEEE Transactions on Communications, 40:917-925, 1992.

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