WIRELESS COMMUNICATIONSYSTEM

REUSE FREQUENCY This concept allows the frequency channel used for a

single cell is used again in other cells.

However, the cells must be far away from each other to avoid interference. Please refer to Figure 4.1. With the use of frequency, cellular system can handle a large number of simultaneous connections, far exceeding the number of channels provided.

Figure 4.1

Figure 4.1 clearly shows the frequency re-use, in which adjacent cells are unlikely to adopt the same frequency, but subsequent cells will use.

Let the frequency allocations for the RBS Q1 - 988.2 MHz, S2 - 988.3 MHz, Q3 - 988.4 MHz, S4 - 988.5 MHz and S5 - 988.6 MHz, then the distribution of these frequencies, it can avoid overlapping with each other.

Next, the frequency can be reused in cells that do not overlap with the frequencies to be reused earlier.

CELL SPLITTING A Cell is the basic geographical unit of a cellular

system. Commonly represented as a hexagon.

The term cellular comes from the hexagonal or honeycomb shape of the coverage area. Each cell has a BS transmitting over a cell. Because of constraints imposed by natural terrain and man made structure .

The true shapes of cell are not hexagonal. The coverage area of cell is called the footprint. The BS simultaneously communicates with many mobile using one channel (pair of frequencies) per mobile.

One frequency is for the forward link (Base station to the mobile) and other frequency is for the reverse link (Mobile to the Base station). Each cell size varies depending on landscape, subscriber density and demand within particular region.

This concept enables large cells divided into small cells equipped with a transmitter (RBS) small power. Thus the repeat distance of frequency reuse to be lower and the number of channels in the area will increase far exceeds the capacity of a large cell of origin, refer to Figure 4.2.

Figure 4.2

This is due to more users in an area. Habit, breaking Tues done in urban areas, where mobile phone use is more widespread.

As a result, more stations and channels RBS provided. This situation clearly we can see in the cities where the density of the cell is higher than rural areas. Refer to Figure 4.3.

Figure 4.3

Cluster. A cluster is a group of cells. No frequencies are reused

within a cluster. Frequencies used in one cell cluster can be reused in another cluster of cells. A large number of cells per cluster arrangement reduces interference to the system.

Frequency reuse. Frequency reuse is a technique of allocating channels

to the cellular system.

Because of the unavailability of the spectrum at the cellular band, channels frequencies must be reused. Cells are assigned group of channels that are completely different from those of neighbouring cells.

Cells with the same number have the same set of frequencies, if the number of available frequency is 7, the frequency reuse factor is 1/7, which implies that each cell is using 1/7 of available frequencies . Frequency reuse introduces interference into the system.

PAGING When you receive a call, your cell phone will alert which

means there is an incoming call.

This process is called paging.

It is a control channel message containing identity Cellular Phone Number (Mobile Identification Number) and indirectly, it tells us that there is an incoming call.

Number sent by the caller to the recipient will be examined by the MTSO (Mobile Telephone Switching Office).

Then, the MTSO will send a signal to all the numbers called other MTSO.

Once the recipient is identified, the MTSO will transmit near Cellular Phone Number for RBS (Radio Base Station) identity of the caller.

RBS will contact numbers called. Recipients will receive a display of the caller number on his cellular phone.

 At the same time, the caller will receive a display of numbers called by RBS it.

HAND - OFF

Handover or Handoff. Refers to the process of transferring an ongoing call

or data session from one channel connected to the core network to another.

In satellite communication it is the process of transferring satellite control responsibility from one earth station to another without loss or interruption of service.

How hand-off or hand-over work? When the user moves out of the cell adjacent to the cell of

origin, he will lose control of radio communications on the channel of cells originally.

Terminals will be adjusted automatically on a Terminals will be adjusted automatically on a new cell control channel.

This process happens so quickly that go unnoticed by the user.

When the conversation is going on, users will hear a beep that moment, when the Hand-Off is done.

RBS MSTO

RBS

   Ke PSTN

SALURAN Kawalan Baru (Hand-Off)

Kedudukan asal telefon bimbit

Kedudukan baru  bagi telefon bimbit

SIGNAL TO NOISE RATIO [SNR] SNR ratio is very important to determine the

effectiveness of the operation or the ability of the cellular system to improve weak signals.

In addition, SNR also able to detect the signal strength compared to the noise that is not needed.

SNR ratio expressed in dB at any SNR (dB) = 10 log Isyarat (S)

Hingar (N)

To obtain a good signal, the ratio should be higher SNR. In which case, the gain of the signal above the noise gain.

CALLING PROCESS

Agaknya macam mana mereka ini boleh berkomunikasi antara selular dengan selular atau selular dengan telefon

A. PSTN To The Mobile Unit.

1. MTSO received a call from the caller via PSTN.

2. MTSO will check digit dialing and determine whether the mobile unit is used or not.

3. If used (on-hook), the MTSO will switch ‘paging’ to guide cellular and attempt to get the free channels and direct tune to that channel.

4. Cellular unit will send a confirmation to the MTSO via RBS channel and then send a call progress tone that produces a ringing.

5. MTSO will stop ringing when it receives a positive signal that the mobile user has answered the call and the conversation can begin.

B. Mobile Unit To PSTN.

1. Cellular users dialing the desired number and press the ‘SEND’. This will cause the number at the dial and cellular dialer will be sent to the MTSO.

2. If the identification number, MTSO will connect the call to the PSTN network. Next to complete the form to the user being call.

3. Using RBS, MTSO will get the channel guide that is free and direct cellular unit to turning to the channel.

4. After the MTSO receives confirmation that the mobile unit tunes, mobile users will receive a progress tone of the MTSO.

5. MTSO will stop ringing when users begin to answer cellular calls and conversations began.

C. Mobile Unit To The Other Mobile Unit.

1. Mobile users who want to call to dial the desired number and press ‘SEND’.

2. MTSO will receive caller identification number and the number is then examined for authenticity and it determines whether the call is to use mobile units (on-hook) or not (off-hook)

3. MTSO will send the command ‘paging’ to all the so-called RBS and users will receive instructions.

4. Positive signal from users who are called will cause the MTSO trying to get the free channels and direct users of both manual turning to their channel. Then the so-called mobile unit will ring.

5. MTSO will stop ringing when the called user to answer and the conversation by both users began.

CALL RELEASE It is a process in which the caller terminate the call.

MTSO will find the new status of the mobile unit which is in normal condition, that it can receive and make another call.

How to release the call made by the mobile unit.

Mobile users call by pressing the 'END'. This information will be sent to RBS and sent to the MTSO.

Upon termination of the signal received by the MTSO, the call to process payments made.

RBS will stop sending information to the correct user and now it is in normal condition.

Mobile users will also stop the delivery of information and try to get the best control channel on a cell.

FREQUENCY SPECTRUM The frequency spectrum of a time-domain signal is a

representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.

Cellular system has been set for the frequency range operation. From Figure 4.5, we can see, the operators A and B are allowed to use a total of 25 MHz of radio spectrum transmitter and receiver set.

From the range of 25 MHz transmitter, it is divided into two parts, the frequency range 12.5 MHz for transmitter operators A and 12.5 MHz for the frequency range of a transmitter for each operator B.

Radio channel used in cellular systems spaced by 30 kHz per channel. Each operator has a range of 12.5 MHz and 12.5 MHz for the transmitter to the receiver.

This means that each operator has a radio channel 416 (12.5 MHz/30 = 416 kHz channel). Of the 416 channels, it is divided into 395 voice channels and 21 channel control.

CELLULAR SYSTEM CONTROL IN MALAYSIA

Syarikat Sistem Frekuensi(MHz) Standard Kod

Celcom ART 900 900 ETACS 010

Time Telekom ATUR 450 450 NMT 011

Maxis Mobile Maxis 900 GSM 012

STM TM Touch 1800 PCN 013

Digi 1800 Digi 1800 1800 PCN 016

Time Cel Time Cel 1800 PCN 017

Mobikom Mobifon 800 800 AMPS 018

Celcom Celcom GSM 930 GSM 019

WAP TECHNOLOGY WAP or Wireless Application Protocol, is a wireless

mobile device, which provides access information directly from the source. Among the mobile devices that can handle WAP technology is mobile phones, pagers, two-way radios, smart phone and communicator.

WAP capable of handling wireless networks such as GSM, PDC, PHS, CDPD, CDMA, TDMA, DataTAC, iDEN and others.

Meanwhile, the operating system that can handle WAP is the PalmOS, EPOC, Windows CE, FLEXOS, OS / 9 and JavaOS.

Therefore, access to information from the WAP is in the form of text, pictures, etc., then the large screen and compact to be provided.

For example, suppose you want to access web pages (internet), then, micro browsers be used to access the page. In this context, the browser brings the purpose of a small file that uses memory (memory) is small.

Thus, the frequency bandwidth of the information will also be small. This facilitates the use of this mobile device.

Companies that are first responsible for the development and growth of WAP technology is Unwired Planet, Nokia, Motorola and Ericsson.