Sharif Digital Repository

In this paper, we propose a distributed rate and power allocation algorithm for real time traffic by using second order statistics of the channel. Our method minimizes the average delay of transmission over the fading channel. We assume that each sub carrier relies on its own buffer, and a constant arrival rate from higher layer application arrives at input buffers of each sub-carrier. This constant rate is optimally distributed through individual sub-rates transmitted over each sub-channel. Optimum power coefficients are also derived to minimize the average delay of transmission. In addition, collision and buffer overflows are taken into account while achieving acceptable throughputs  

In this paper we study slotted ALOHA random access optical code division multiple access packet-switching networks with a chip-level receiver structure. We use generalized optical orthogonal codes (GOOCs) and the overlapping pulse position modulation (OPPM) signaling technique to improve system performance. The impact of physical layer parameters such as the GOOC cross-correlation value and the OPPM overlapping index on key performance benchmarks such as network throughput and delay are analyzed. We also study the stability of the network based on the number of backlogged users, using the expected state drift. It has been shown that using GOOC instead of strict optical orthogonal codes... 

In this paper, we propose a new packet prioritization scheme in order to exploit the full-duplex (FD) capability of the access point (AP) more efficiently, in an asymmetric IEEE 802.11-based WLAN, i.e., only the AP has the in-band FD communications capability. In this respect, we consider a modified version of IEEE 802.11 MAC protocol such that at any transmission opportunity in which AP has the role of the transmitter or the receiver, it does the best to select a partner packet to be simultaneously received or transmitted, respectively. The key feature of our proposed partner packet selection scheme is to reduce the idle time intervals that in an FD transmission opportunity, due to... 

Intermittent connectivity is an intrinsic feature of vehicular ad hoc networks (VANETs) in sparse situations. This type of network is in fact an example of delay and disruption tolerant networks (DTNs). In this paper, we focus on a typical two-way street and analytically evaluate the maximum stable throughput and the average delay for packet forwarding along the street. To this end, we map the mobility patterns of the vehicles with different speeds onto suitable parameters of a BCMP queueing network and derive the location density of vehicles. Then, we employ another queueing network in order to model opportunistic multi-hop packet forwarding along the street with respect to the... 

In this paper, we propose the Object Pursuing based Efficient Routing Algorithm (OPERA) suitable for vehicular ad hoc networks (VANETs), esp. in sparse situations. The proposed algorithm is applicable for both moving and fixed destinations. It is based on considering static nodes at each intersection. In this algorithm, we optimize the decision making at intersections, with respect to the connectivity and feasibilty of the roads. To this end, we consider the average delay of each road as the connectivity metric, and the vehicle availability in the transmission range of the intersection as the feasibility metric. By exploiting the related metrics, we select the next road to forward the packet... 

To help overcome limits to the density and speed of conventional SRAMs, we have developed a five-transistor SRAM cell. The newly developed CMOS five-transistor SRAM cell uses one word-line and one bit-line during read/write operation. This cell retains its data with leakage current and positive feedback without refresh cycle. The new cell size is 18% smaller than a conventional six-transistor SRAM cell using same design rules. Simulation result in standard 0.25μm CMOS technology shows purposed cell has correct operation during read/write and idle mode. The average delay of new cell is 20% smaller than a six-transistor SRAM cell. © 2008 IEEE  

In this paper we present a semiclassical model for explanation of the nonlinear optical effect and phase matching. We calculate momentary quantities of the delay time of photon-electron interaction in each layer. We show that for phase matching, the average delay time for the fundamental photons must be equal to the average delay time for the harmonic photons. Additionally, we calculate the number of layers that the harmonic photon needs to be absorbed or converted to fundamental photons. This calculation applies to different wavelengths with different phase matching angles. Our simulation results are in good agreement with experimental data. © 2008 IOP Publishing Ltd  

In this paper, we analyze the effect of applying leaky bucket as a well known traffic shaper on data users in a variable spreading gain CDMA (VSG-CDMA) uplink wireless cellular network. To this end, we model the effect of leaky bucket mechanism on a typical data user, with a closed product form queueing network. Each node in this queueing network corresponds to a specific processing gain or equivalently transmission rate and power. By solving such a queueing network we obtain the steady state probability with which a typical data user will exist at each node. By aggregating the effects of all data users we compute the mean and variance of interference and obtain the throughput and average...