Standards – Page 8

July 6, 2011March 6, 2013Capacity, LTE

Shannon Capacity of LTE (Effective)

In the previous post we calculated the Shannon Capacity of LTE as a function of bandwidth. We now calculate the capacity as a function of SNR (bandwidth fixed at 20MHz and signal power varied). We also use the concept of effective bandwidth to get a more realistic estimate of the capacity. The modified Shannon Capacity formula is given as: C=B_eff*log2(1+SNR) where B_eff=Bandwidth*eff1*eff2*eff3*eff4 eff1=0.9=due to adjacent channel leakage ratio and practical filter issues eff2=0.93=due to cyclic prefix eff3=0.94=due to pilot assisted channel estimation eff4=0.715=due to signalling overhead B_eff=0.57*B Therefore C=0.57*B*log2(1+SNR) Note: This is the capacity in a SISO channel with no […]

July 6, 2011January 9, 2013Capacity, Channel Capacity, Fundamentals, LTE

Shannon Capacity of LTE (Ideal)

Shannon Capacity of LTE in AWGN can be calculated by using the Shannon Capacity formula: C=B*log2(1+SNR) or C=B*log2(1+P/(B*No)) The signal power P is set at -90dBm, the Noise Power Spectral Density No is set at 4.04e-21 W/Hz (-174dBm/Hz) and the bandwidth is varied from 1.25MHz to 20MHz. It is seen that the capacity increases from about 10Mbps to above 70Mbps as the bandwidth is varied from 1.25MHz to 20MHz (keeping the signal power constant). It must be noted that this is the capacity with a single transmit and single receive antenna (MIMO capacity would obviously be higher).

June 22, 2011August 8, 2011Capacity, WCDMA

WCDMA Uplink Capacity (N-pole)

The uplink capacity of a WCDMA cell also known as the pole capacity is given as: N=(W/R)/((Eb/Nt)*v*(1+a)) where 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 […]

June 21, 2011November 15, 2011Capacity, WCDMA

CDMA vs FDMA Capacity (Mbps)

We saw previously that the channel capacity of a WCDMA system is severely limited by the Multiple Access Interference (MAI). Now let us consider the case where the 5MHz channel is divided equally among 20 users such that each user has a bandwidth of 250kHz. Keeping the transmit power for the narrow band signal the same as the wideband signal the signal to noise ratio would improve tremendously (since there is no MAI and the noise power is reduced by a factor of 20). Thus each narrowband channel would have a capacity of 2.99Mbps giving a combined capacity of 59.83Mbps […]

June 20, 2011August 23, 2011Capacity, WCDMA

WCDMA Capacity (Mbps)

The capacity of any wireless communication channel is given by the well known Shannon Capacity Theorem: C=B*log2(1+SNR) or C=B*log2(1+P/(NoB)) where C is the capacity of the channel in bits/sec, P in the noise power in Watts, No is the noise power spectral density in Watts/Hz and B is the channel bandwidth in Hz. It is obvious that the channel capacity increases with increase in signal power. However, the relationship with bandwidth is a bit complicated. The increase in bandwidth decreases the SNR (keeping the signal power and noise power spectral density same). Therefore the capacity does not increase linearly with […]

May 30, 2011August 23, 2011WiFi, WiMAX

Laptop Orientation and Data Rate

I live in a basement and do not get very strong WiMAX signals so I have placed my WiFi router outside my home. Now the distance between my laptop (Toshiba Satellite L645) and the WiFi router is larger than I would like it to be. I noticed that the download speed that I get is highly dependent on the orientation of my laptop. So here are the results of download speeds for various antenna orientations. So I am assuming that there is some sort of surface antenna on this laptop that works well in certain directions but does not work […]