We have previously looked at the antennas inside a cell phone. Now we look at another important component of a cell phone; the mobile station modem (MSM). One of the most popular MSM in cell phones today is the Qualcomm Snapdragon S4. The details of this MSM are given in the table below.
As can be seen from the above table this small chipset (can easily fit on a fingertip) packs a punch as far as processing power is concerned. It supports a number of wireless standards from GSM/GPRS to LTE and from CDMA 2000 to TD-SCDMA. One of its close competitors is the NVIDIA Tegra 3 which has four ARM Cortex A9 cores (compared to Snapdragon’s two).
The uplink capacity of a WCDMA cell also known as the pole capacity is given as:
W is the spreading bandwidth fixed at 3.84MHz
R is the radio access bearer bit rate e.g. 12.2kbps
Eb/Nt is the energy per bit to noise power spectral density ratio e.g. 5dB
v is the voice activity factor which depends upon the vocoder, channel coding and actual application e.g. 0.5
a is the other-cell to in-cell interference ratio e.g. 0.65
Using the above values the pole capacity of the WCDMA cell is calculated as 120. In the case of a mobile UE (3km/hr) the required Eb/Nt may be as high as 12dB resulting in pole capacity of 24. The actual capacity is obtained by multiplying the pole capacity with network loading factor which maybe taken as 0.75 in this example resulting in an uplink capacity of 18.