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This paper deals with the wireless personal area networks. It works in small area for delivering multimedia traffic. The IEEE 802.15.3 is the emerging standard for WPAN. This standard is designed to provide low complexity, low cost and low power-consumption for personal area networks that manage multimedia traffic, video and audio between different devices in a small area environment. In this, system aims to maximize the performance of the WPAN in terms of throughput, considering multimedia traffic, constituted by data and video traffic. And the piconet topology issues in IEEE802.15.3 High Rate Wireless Personal Area Network standard.
In this an improvement in the small area network deployment was due to the introduction of the Ultra Wide Band (UWB) technology , that differs from previous communication systems for the use of radio impulses that allow to have an ultra wide bandwidth occupation with low power emissions, leading to high data rate transmissions.
A WPAN (wireless personal area network) is a personal area network a network for interconnecting devices centered around an individual person's workspace in which the connections are wireless. Typically, a wireless personal area network uses some technology that permits communication within about 10 meters in other words, a very short range. One such technology is Bluetooth, which was used as the basis for a new standard, IEEE 802.15.3A WPAN could serve to interconnect all the ordinary computing and communicating devices that many people have on their desk or carry with them today or it could serve a more specialized purpose such as allowing the surgeon and other team members to communicate during an operation.
A key concept in WPAN technology is known as "plugging in". In the ideal scenario, when any two WPAN equipped devices come into close proximity (within several meters of each other) or within a few kilometers of a central server, they can communicate as if connected by a cable. Another important feature is the ability of each device to lock out other devices selectively, preventing needless interference or unauthorized access to information The technology for WPANs is in its infancy and is undergoing rapid development. Proposed operating frequencies are around 2.4Â GHz in digital modes. The objective is to facilitate seamless operation among home or business devices and systems. Every device in a WPAN will be able to plug in to any other device in the same WPAN, provided they are within physical range of one another. In addition, WPANs worldwide will be interconnected. Thus, for example, an archeologist on site in Greece might use a PDA to directly access databases at the University of Minnesota in Minneapolis, and to transmit findings to that database.
IEEE 802.15.3.a(WPAN High Rate Alternative PHY& MAC Amendment):
IEEE 802.15.3-2003 is a MAC and PHY standard for high-rate (11 to 55 Mbit/s) WPANs.IEEE 802.15.3a was an attempt to provide a higher speed UWB PHY enhancement amendment to IEEE 802.15.3 for applications which involve imaging and multimedia. The members of the task group were not able to come to an agreement choosing between two technology proposals, Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) and Direct Sequence UWB (DS-UWB), on the table backed by two different industry alliances and was withdrawn in January 2006.
Ultra-Wideband (UWB) is a technology for transmitting information spread over a large bandwidth (>500 MHz) that should, in theory and under the right circumstances, be able to share spectrum with other users. Regulatory settings of FCC are intended to provide an efficient use of scarce radio bandwidth while enabling both high data rate "personal area network" (PAN) wireless connectivity and longer range, low data rate applications as well as radar and imaging systems.
Ultra Wideband was traditionally accepted as pulse radio, but the FCC and ITU-R now define UWB in terms of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of 500 MHz or 20% of the center frequency. Thus, pulse-based systems where in each transmitted pulse instantaneously occupies the UWB bandwidth, or an aggregation of at least 500 MHz worth of narrow band carriers, for example in orthogonal frequency division multiplexing (OFDM) fashion can gain access to the UWB spectrum under the rules. Pulse repetition rates may be either low or very high. Pulse-based UWB radars and imaging systems tend to use low repetition rates, typically in the range of 1 to 100 megapulses per second. On the other hand, communications systems favor high repetition rates, typically in the range of 1 to 2 giga-pulses per second, thus enabling short range gigabit per second communications systems. Each pulse in a pulse-based UWB system occupies the entire UWB bandwidth, thus reaping the benefits of relative immunity to multipath fading (but not to intersymbol interference), unlike carrier-based systems that are subject to both deep fades and intersymbol interference.
Piconet is the basic topology used in the IEEE802.15.3 system. A typical 802.15.3 network topology is depicted in Piconet topology is based on the master/slave paradigm firstly introduced by the Bluetooth system. Here the master device is named PicoNet Coordinator (PNC) and slaves are simply designated as simple DEVices (DEV). A piconet encompasses exactly one PNC and up to 236 DEVs. Two DEVs included in the same piconet can exchange data directly. Four co-located piconets can operate without interference in the 2.4 GHz frequency band thanks to the set of four channels that is defined. Two piconets and one IEEE802.11b system can coexist without interference in the same area thanks to the three channel set defined for this purpose. There are two co-located piconets. They are set-ups on two different channels. PNC1 and PNC2 coordinate the piconets on channel #1 and channel #2 respectively. Because DEV1,1 and DEV3, belong to the same piconet, they can exchange data; similarly for DEV2,2 and DEV0,2 (which is also PNC2).A DEV that wants to become PNC must follow four steps.
First, the DEV scans all available channels. Second, it chooses free channel. Third, it stays listening to the selected channel for a period of time to be sure channel is free. And finally, ifselected channel is free, the device becomes PNC and starts tobroadcast beacons.Within a piconet, time is divided into superframes. Typicalscheme of a superframe structure is shown in Asuperframe is made of three parts. First part is the beacon. The beacon allows DEVs to synchronize to a piconet and contains piconet information (piconet identifier, superframe duration, and channel time allocations). The second part of thesuperframe is the Contention Access Period (CAP). The CAP can be used for signaling messages as well as small data
transfers. Channel access in CAP is based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance).Third part is the Contention Free access Period (CFP). Channel access in CFP is based on TDMA (Time Division MultipleAccess) mechanism. CFP is divided into slots named Channel Time Allocation (CTA) slots. CTAs can be used for commands transmitted to or from the PNC (MCTA Management Channel Time Allocation slots) or for data (CTA). CFP slotsare managed by the PNC. Size of the CAP and CFP may vary according to channel time needs and the CAP can be replacedby exclusive use of MCTAs.If a device wants to establish a piconet and finds all thechannels busy, it can request an established piconet to create adependent piconet. A dependent piconet requires a timeallocation in another piconet (parent piconet) and is synchronized with the parent's timing. They are two types of dependent piconets. First, a child piconet is a dependentpiconet where the PNC is member of the parent piconet.Second, a neighbor piconet is a dependent piconet where the PNC is not member of the parent piconet. There are two piconets. Parent piconet and child piconet operate over the same channel. There is a reserved period of time in the parent super frame (respectively child super frame) that allows child PNC (respectively parent PNC) to broadcast its beacon allocate its own CAP and a CFP. A DEV included in child piconet (respectively parent piconet) can not exchange data directly with a DEV in parent piconet (respectively child piconet) except if it belongs to the two piconets. An example is provided via DEV4, which acts as an ordinary DEV in parent piconet and as PNC in the child piconet.If a DEV wants to be included into an existing piconet, it has to follow three steps. After scanning all the available channels, it must select a channel where there is an establishedpiconet. Finally, it joins the selected piconet by sending an association request. Once a DEV is associated, it can request channel time to exchange data by sending a message request tothe PNC.If the PNC decides to stop its piconet, it can operate a PNC handover. If no PNC-capable DEV is found in current piconet,it simply stops to broadcast beacons. A PNC handover can alsobe performed at any time i.e. when a new DEV joins the piconet. DEVs can leave a piconet at any time by sending a disassociation request to the PNC.
In this Section, the numerical results obtained via computer simulation will be shown. By them it is possible to validate the proposed scheduling algorithm for an UWB based WPAN that
uses the IEEE 802.15.3a standard. In particular it is possible tosee how the proposed technique can improve the performanceof a piconet in the case of multimedia traffic. For our purpose
we have considered a communication scenario with best-effort(WWW) data traffic and MPEG1 video traffic.Even if in IEEE 802.15.3a it is possible to use a very highbit-rate, we have considered, due to computational capabilities,to use a physical channel supporting 11 Mbit/s. The numerical results have been obtained with the following parameters:
â€¢ One slot is composed by 512 byte and it lasts 3.5 Î¼s;
â€¢ One superframe is composed by 200 slots and it lasts70 ms;
â€¢ The command frame lasts 2 slots;
â€¢ The beacon frame lasts 3 slots;
â€¢ NminMTSiis equal to 2 slots.
As said before, it has been supposed that two type of data traffics are present in the piconet. The first one is useful for modeling the web traffic and it is based on the joint use of a Poisson statistic for the message interarrival and a trunked P are to for the message length, having a p.d.f.:
f(x) =Î± k Î±
xÎ±+1, kâ‰¤ x < m
k Î± m Î±, x= m
0 x < k or x > m
where Î±=1.1 is the shape parameter, k=1858 bytes is the location parameter (corresponding to the minimum message length), and m = 5Â·10 6 bytes is the maximum message length.By using the above parameters the average message length is about 12KB .
The idea behind the optimal MTS management is that, whethe traffic condition is heavy, it is better to use more the Contention Free Period (CFP) while in the case of weak traffic conditions, it could be better to use more the Contention AccessPeriod (CAP), that, despite a contention based access, doesnot need to notify the PNC of a new transmission, lowering so the management traffic. In the optimal MTS management,it has been calculated via computer simulations the optimal value of NminCAP and NmaxCAPi for minimizing the queue delay in each device. The outlined optimization process can be easily implemented by each node also in real scenario considering that each one can calculate the delay of each message in the queue; the device communicates it to the PNC, approaching the optimal management in a distributed way.
it is shown the performance in terms of throughput for the optimal MTS management by considering the presenceor not of control messages. It is possible to see that, even if theoptimal policy increases the management messages the loss interms of throughput is negligible.
It has been then considered the presence of GTS; in particular has been done a performance comparison in terms of throughput and delay in the case of only web traffic, considering
to use only GTS or only MTS with the optimal management technique. The number of GTS is supposed to 12 in order to make possible the communication of all the four active devices
between them by using GTS channel itis possible to improve the performance in terms of throughput, but this leads to a not allowable delay increase. This is due to the fact that even if the use of GTS leads to a simplified frame management, the fixed length cannot follows the traffic behaviour, increasing so the delay performance.
In the case of the throughput, the comparison has been made also with the maximum throughput case, in which all the messages have been supposed to be sent without delay, that corresponds to:
Î· = Nl Â· Tslot/T
where N is the number of active devices in the piconet, l is the average message length in slots, Tslot is the slot duration and T is the average message interarrival time. It is possible to see how the proposed optimal MTS length management outperform the other techniques in terms of throughput and delay, allowing an almost ideal throughput performance with a sensibly lower delay.
The interest to the WPAN is emerging in the last years due to the growing interest in multimedia communication scenarios. A MAC technique that takes into account the amountof data in each device has been proposed; an optimized version has been also considered showing the improvement in performancein terms of throughput allowable. Finally the case of areal scenario with data and video traffic present at the sametime has been considered, showing the good performance of the proposed approach.