Presented by : Er. Amit Mahajan

Comparative Analysis of Frequency Allocation and Frequency Reuse in

GSM , CDMA and W-CDMA

CELLULAR FREQUENCIES

All cellular phone networks worldwide utilize a portion of the radio frequency spectrum designated as Ultra High Frequency, or "UHF“(300MHz-2400MHz ), for the transmission and reception of their signals. The UHF band is also shared with Television, Wi-Fi and Bluetooth transmission. The cellular frequencies are the sets of frequency ranges within the UHF band that have been allocated for cellular phone use.

eg. AMPS - 800 MHz

GSM- 850/900/1800/1900 MHz

Frequency Ranges

ELF (Extreme Low Frequency) 3Hz-30Hz (Sub Audible Range) SLF (Super Low Frequency) 30Hz-300Hz (Low Frequency Voice) ULF (Ultra Low Frequency) 300Hz-3000Hz (Telephonic Voice Range) VLF (Very Low Frequency) 3KHz-30KHz (Audible Range) LF (Low Frequency) 30KHz-300KHZ (Ultra Sounds) MF (Medium Frequency) 300KHz-3000KHz (AM Radio long range) HF (High Frequency) 3MHz-30MHZ VHF (Very High Frequency) 30MHz-300MHz (FM Transmissions short range) UHF (Ultra High Frequency) 300MHz-2400MHz (Mobile Communications GSM and

CDMA) SHF (Super High Frequency) 2.4GHz-30GHz (Wi-Fi and Wi-Max Broadband

wireless) EHF (Extremely High Frequency) 30 GHz-300GHz (Point to Point Microwaves)

Frequency Choice

The effect of frequency on cell coverage means that different frequencies serve better for different uses. Low frequencies, such as 450 MHz NMT, serve very well for countryside coverage. GSM 900 (900 MHz) is a suitable solution for light urban coverage. GSM 1800 (1.8 GHz) starts to be limited by structural walls. This is a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity.

Cell service area may also vary due to interference from transmitting systems, both within and around that cell. This is true especially in CDMA based systems.

Frequency bands used in the U.S:

GSM Frequency Bands: There are 14 bands defined in 3GPP

P-GSM, Standard or

Primary GSM-900 Band E-GSM, Extended GSM-900

Band (includes Standard GSM-

900 band) R-GSM, Railways GSM-

900 Band (includes Standard

and Extended GSM-900 band)

CDMA Frequency Bands

IMT-2ooo(WCDMA) Freq. Band in 800 & 2000 MHz

Frequency Reuse Principle

The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission.

Cellular telephone systems rely on an intelligent allocation and reuse of channels. Each base station is given a group of radio channels to be used within a cell. Base stations in neighboring cells are assigned completely different set of channel frequencies. By limiting the coverage areas, called footprints, within cell boundaries, the same set of channels may be used to cover different cells separated from one another by a distance large enough to keep interference level within tolerable limits.

Reuse Factor

The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation). In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3. A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site.

Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM).

If the total available bandwidth is B, each cell can only utilize a number of frequency channels corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.

Fraction of total available channels assigned to each cell within a cluster is 1/N.

(a) Cells showing reuse factor of ¼, (b) Cells showing reuse factor of 1/7 .

As the demand increases in a particular region, the number of stations can be increased by replacing a cell with a cluster as shown in Fig. 2.2. Here cell C has been replaced with a cluster. However, this will be possible only by decreasing the transmitting power of the base stations to avoid interference.

Shannon Theorem:

C = W [(log2(1+SIR)] / Reuse factor where as C: Channel capacity, W: Total bandwidth

Cell Edge SIR at Different Reuse Factor.

Cell Edge Channel Capacity at Different Reuse Factor.

Where K is the frequency

reuse pattern D = 3.46R K= 4 4.6R K= 7 6R K= 12 7.55R K= 19

Frequency Reuse Distance:D = √3K R

Design Objectives for Cluster Size

High spectrum efficiency many users per cell small cluster size gives much bandwidth per cell High performance Little interference

Cell Sizes : Macro-cellular 1 - 30 km Micro-cellular 200 - 2000 m Pico-cellular 4 - 200 meter

The effect of decreasing cell size

Increased user capacity Increased number of handovers per call Increased complexity in locating the subscriber Lower power consumption in mobile terminal: Longer talk time, Safer operation Different propagation environment, shorter delay spreads Different cell layout lower path loss exponent, more interference more difficult to predict and plan more flexible, self-organizing system needed.

Cell Splitting:

If the cellular system contains N cells with total allocation of C channel , then each cell will contain SC/N channels .To grow further from the capacity S , the cell boundaries has to be revised so that each cell now contains several cells. This process is called cell splitting.

 Interference with other cells:Co-channel interference: Transmission on same

frequency.Adjacent channel interference: Transmission on

close frequencies.

Cell Splitting and Adjacent Channel Interference

Frequency Reuse in GSM and CDMA

CDMA based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated for by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 1/1. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. While N is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually.

Differences between WCDMA and GSM Networks.

SIMULATION RESULTS FOR PLANNING

An area of 3500 Km2 radius of 3km has been taken as an example.

Four cases as an optimization has been calculated : without cluster, with clusters 7,9,13.

Limitations on frequency reuse:

Frequency reuse is limited by the tolerable SIRmin

SIRmin is determined by the modulation characteristics of the radio system

First generation analog systems (AMPS)

SIRmin= 18dB

Second generation digital AMPS

SIRmin= 14dB

European GSM

SIRmin= 7-12dB

Reference:

1. http://www.site.uottawa.ca/~ivan/hybrid-ca.pdf2. http://www.3gpp.org/ Over-The-Air%20Provisoning%20in

%20WCDMA.pdf3. http://en.wikipedia.org/wiki/Cellular_networks4. http://www.elec.york.ac.uk/comms/pdfs/

20030502165327.pdf5. “Fundamentals of Wireless Communication” by David Tse

and Pramod Viswanath.