Wireless Networks have a limited bandwidth the uses that have been sharing this bandwidth have been increasing over the years, however the SDMA technique which allows the using of directional antennas to increase the ability of wireless networks by dividing all used by 2.
Which mean the wireless networks capacity can be increased while the delay is decreased by the means of directional antennas using OPNET. Simulation results shows that the performance of using directional antennas is the same as using omnidirectional antennas.
However directional antennas are enable to reduce multipath and co-channel interference by focusing the radiation in one direction for higher capacity, the goal of using directional antennas is to maximize the performance of wireless networks by maximizing the rang and Signal-to-Interference-Plus-Noise Ratio (SNR).
Directional antennas maximize radiated power because there focus there transmission power to one direction which improves the rang of the transmitter. Were the antenna canceling any interfering signal the come from another direction which means more power to the signal strength.
Wednesday, September 9, 2009
Saturday, September 5, 2009
AMPS
image via google images
The AMPS was designed for voice transmission is a technology that is used to allow data over the same voice channels with a frequency of 800 MHz. The cellular data transfer needs a connection between every end just like a voice session. During this connection the cellular data transmission sends data over the airlink (through a PSTN (Public Switched Telephone Network)) to the remote computer.
For a well cellular phone have been utilize radio signals originally radio performance losses signals because of interference of noise and channel degradation which affect data transmission. Therefore ETC (Enhanced Throughtput Cellular) have been introduced to control data compression, error correction and modulation to provide faster reliable transmission along with MNP(Mircrocom Network Protocol)..
The AMPS was designed for voice transmission is a technology that is used to allow data over the same voice channels with a frequency of 800 MHz. The cellular data transfer needs a connection between every end just like a voice session. During this connection the cellular data transmission sends data over the airlink (through a PSTN (Public Switched Telephone Network)) to the remote computer.
For a well cellular phone have been utilize radio signals originally radio performance losses signals because of interference of noise and channel degradation which affect data transmission. Therefore ETC (Enhanced Throughtput Cellular) have been introduced to control data compression, error correction and modulation to provide faster reliable transmission along with MNP(Mircrocom Network Protocol)..
Thursday, September 3, 2009
The Basic Access Method: CSMA/CA
The Distributed Coordination Function essentially Carrier a Sense Multiplying Access with Collision Avoidance mechanism (also known as CSMA/CA). CSMA protocols are one of the most known protocols in the industry, where the most common one is Ethernet which refers to CSMA/CD protocol (CD standing for Collision Detection).
The CSMA protocol works as A station that transmit senses to the medium if the medium is not responding or some other station is transmitting then the medium will continue transmission at a later stage if the medium is sensed free then the station will accept transmission
The following protocol are very effective when the medium is not heavily saturated, because it allows stations to transmit with minimum delay, but there is always a chance that there is another stations transmitting at the same time because of another stations sensed the medium free and decided to transmit (collision).
In this case the collision must be identified so that the MAC layer could retransmit the packet individually and not by the upper layers which may cause significant delay. The Ethernet collision is identified by transmitting stations that goes thought the retransmission stage based on the exponential random backoff algorithm.
These Collision Detecting mechanism are good for wire LAN and cannot be used on WIreless LAN.
So how do we over come this problems.....
The CSMA protocol works as A station that transmit senses to the medium if the medium is not responding or some other station is transmitting then the medium will continue transmission at a later stage if the medium is sensed free then the station will accept transmission
The following protocol are very effective when the medium is not heavily saturated, because it allows stations to transmit with minimum delay, but there is always a chance that there is another stations transmitting at the same time because of another stations sensed the medium free and decided to transmit (collision).
In this case the collision must be identified so that the MAC layer could retransmit the packet individually and not by the upper layers which may cause significant delay. The Ethernet collision is identified by transmitting stations that goes thought the retransmission stage based on the exponential random backoff algorithm.
These Collision Detecting mechanism are good for wire LAN and cannot be used on WIreless LAN.
So how do we over come this problems.....
IEEE 802.11 Architecture
image via google images
An 802.11 LAN derived from cellular architecture where the system is divided into cells, where each cell (Basic Services/ BSS in the 802.11) is controlled by the Main Station or Access Point (AP)
though a wireless LAN may be formed by a single cell, with a single Access Point it can also work without an Access Point. some installations will be formed by several cells, where the Access Point are connected to some kind of backbone (Distribution System) Ethernet or even wireless.
The interconnected Wireless LAN including different cells and there
respective Access Point with the Distribution System in most case always set to the upper layer of the OSI model, a single 802 network is called as Extended Service Set (ESS)
The picture shows a typical 802.11 LAN
The ESS also defines the concept of Portal, a Portal is a device that interconnects with two networks a 802.11 and another 802 LAN. This concept is an abstract description of the "translation bridge"
An 802.11 LAN derived from cellular architecture where the system is divided into cells, where each cell (Basic Services/ BSS in the 802.11) is controlled by the Main Station or Access Point (AP)though a wireless LAN may be formed by a single cell, with a single Access Point it can also work without an Access Point. some installations will be formed by several cells, where the Access Point are connected to some kind of backbone (Distribution System) Ethernet or even wireless.
The interconnected Wireless LAN including different cells and there
respective Access Point with the Distribution System in most case always set to the upper layer of the OSI model, a single 802 network is called as Extended Service Set (ESS)
The picture shows a typical 802.11 LAN
The ESS also defines the concept of Portal, a Portal is a device that interconnects with two networks a 802.11 and another 802 LAN. This concept is an abstract description of the "translation bridge"
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