IJCST Vol. 8, ISSue 2, AprIl - June 2017 ISSN : 0976-8491 (Online) | ISSN : 2229-4333 (Print)

w w w . i j c s t . c o m 32 INterNatIONal JOurNal Of COmPuter SCIeNCe aNd teChNOlOgy

Comparative Study of the Random Access Protocols Slotted ALOHA/CDMA Mode and CPCH/W-CDMA Mode

1Kapil Raj Dhaybhai, 2Dr Sanjay Agal1,2Rajasthan Technical University, Kota, Rajasthan, India

AbstractThe purpose of this paper is to compare the random access protocols Slotted ALOHA / CDMA mode (used in the GSM since January 2000) and CPCH / W-CDMA mode (used in the future UMTS cellular network).The objective is trying to determine which protocol appears to be the most robust to the scalability of clients simultaneously connected to a cell. To compare these two protocols, modeling in the environment Opnet will simulate the operation of the access to UMTS.

KeywordsSlotted ALOHA, CPCH / W-CDMA, OPNET, UMTS

I. The ModelingThe modeling will be to simulate the load induced by several Terminal Equipment (UE) Wireless attempting to connect to a database (BTS) based on two separate access protocols.

Fig. 1:

A. General for ModelingVariables Below is the list of core values that allow us to set our simulations. These variables are called PROMOTED, which means that we can grasp value for each simulation, thus varying the context of simulation to better compare Slotted ALOHA CPCH.LABEL DEFINED IN DESCRIPTION

Cpch_flag QueueAllows simulation Slotted-ALOHA mode (0) and mode CPCH (1).

Interarrival_Time GeneratorAverage value for the draw of the inter time between Packet transmission.

Waiting_Time Queue Time constant before retransmitting a packet.

Max_Retrans_Time Queue

Upper bound of the uniform law used to draw random time before re-emission (in addition to Waiting_Time).

1. Modeling TimeThe basic unit of simulation time slot (0.577 μ s for UMTS). In reality the synchronization between the cell and the issuer must be made despite of the signal propagation times which vary according to distance between the transmitter antenna of the cell. OPNET Modeler guarantees perfect synchronization in the timing of events generated.

2. Modeling of Transmitted Messages (Packets)

Each package used in the simulation contain information following:

id: Sequential identifier of the packet• Emission time: package birthdate: it is a simple timestamp.• Type: Power preamble collision preamble or data.• failure: fail count that led to the reissue package• Power: packet transmission power level.• Priority: the packet priority.• Size: size of the package.• Generated time: date of the last entry on the scene of the • package. It maybe just the date of issue, or if it has been reissued date his last reissue.

II. The Node Model Project

The Node Model of the UMTS project

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The node "generator that sends packets produced" tail "process via the bus type "packet stream".

A. Modeling Issuers (Clients)

1. Automate GeneratorTo ensure a fair comparison between SLOTTED ALOHA and the CPCH generator is the same for the two basic types (same PLC same random sequences of packets sent to bases). The modeling software generates events in strict sequentially, it is not necessary to manage a process transmitter. This is Therefore we will only have a process to manage n transmitters.

We can vary the number of client, ie the network load, modifying the constant INTERARRIVAL_TIME (Promoted). The generator transmits packets according to a time interval which follows a law fish.

At a given time, the number of transmitters that transmit simultaneously is pulled random (exponential reason 2). Representation of finite state machines of the node "generator".

B. Modeling base Slotted ALOHA

1. Automate cell Slotted ALOHA

2. Etat STOPThis state is reached on stopping the simulation. Ensures free the memory resources. NB: the Sorted Tail is always keep in mind the package that will be reissued in first.

C. Modeling the CPCH ProtocolSee slotted-ALOHA modeling (with variable Promoted Cpch_flag = 1).

III. Simulations

A. Test ScenariosEight scenarios were used to test each of the protocols. Here is the detail setting for each of them:

So, we will have 8 different simulations for each observed variable.

B. Statistics CollectedDuring the study, we observed the following parameters compare the two access protocols:

1. Percentage Packet Received/Generated Packets

This curve shows that the volume of packets between the two protocols is comparable. It also provides information on the magnitude of generated packets depending on the inter arrival.

2. Packet Received Following the Inter Arrival

IJCST Vol. 8, ISSue 2, AprIl - June 2017 ISSN : 0976-8491 (Online) | ISSN : 2229-4333 (Print)

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3. Percentage Packet Received/Generated Packets

4. Temps Average Wait Per Pack

5. Number Using Packet Preambles

6. Percent Packet Loss/Generated Packets

7. Average Waiting Time Per Pack

IV. ConclusionDifferences between slotted-ALOHA and CPCH is not as marked as we would have been expected. CPCH provides a real advantage regarding transmission times. This is explained by the fact que la power of collision preamble frames are destroyed, thereby releasing the network resource, while in the frame ALOHA Data is reissued.

Slightly less effective CPCH Appears When The network is loaded. As the packets are destroyed, It Has less packets sent with success.

The simulation gives no indication regarding the flows. Or priori in this case, CPCH Should be significantly better. In fact, the frames data is much larger in volume than the total Preamble. ALOHA May need to Log retransmit data frames while Ensures CPCH que la Transmitted Data Will Be No frame collision.

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