# Analysis Of Qos Analysis Of 4G And 3G

Abstract— The cellular communication system performance is improved by increasing channel capacity and spectrum efficiency. Spectral efficiency (SE) is a key factor in the design of cellular communication system as it quantifies how well the limited frequency spectrum resource is utilized. The efficient use of spectrum is analyzed in terms of coverage area, capacity and reuse distance. OFDMA is a very potential multiple access technique, which will be the key technique for the next generation of wireless communications (4G). In this paper the QoS parameters of OFDMA i.e. spectral efficiency [Erlangs/MHz/m2], system capacity is estimated and also compared with the WCDMA. The other important parameters

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Therefore, the SINR in an OFDM system is depend on the other-cell interference and the background noise [4], [5]. The SINR in an OFDM system can be expressed as: Where S=Received power,

N0=thermal Noise,

If is the ratio between other-cell and own-cell signal.

The capacity limit of an OFDM system is given as: b/s/Hz

Where B is the Band width of the system

In OFDMA by the consideration of the cyclic prefix overhead, the capacity of an OFDM system is modified as: b/s/Hz

Where Ds is the OFDM symbol duration and

Dc is the cyclic prefix duration. Then capacity of OFDMA system b/s/Hz (4)

III. AIR INTERFACE CAPACITY AND SIGNAL DEGRADATION IN OFDMA

A. Air interference capacity of OFDMA system

The air interface capacity of an OFDMA system is expressed in terms of number of subscribers [6]. The total cell capacity (total number of subscribers in a cell) with Quality of Service (QoS) can be expressed as Where Ko is over subscribe factor,

Ns is number of sectors in a cell,

S is link efficiency,

B is bandwidth if the system,

Lbh is busy hour loading and

R is data rate.

In LTE systems OFDMA is used in the downlink. Hence the above equation can be modified as (5)