How does WCDMA cope with interference and fading compared to GSM?

1 What is interference and fading?

Interference and fading are two phenomena that degrade the quality and reliability of wireless signals. Interference occurs when multiple signals share the same frequency band and cause distortion or noise. Fading occurs when the signal strength varies due to multipath propagation, distance, or obstacles. Both interference and fading can result in errors, delays, or dropped calls.

2 How does WCDMA handle interference?

WCDMA stands for wideband code division multiple access, which means that it uses a wide frequency band and assigns a unique code to each user or channel. The codes are orthogonal, meaning that they are independent and do not interfere with each other. The receiver can separate the desired signal from the others by using the same code. This allows WCDMA to support multiple users and services in the same band, and to adapt to the changing interference conditions.

3 How does WCDMA handle fading?

WCDMA also uses adaptive modulation and coding (AMC) to cope with fading. AMC means that the transmitter can adjust the modulation scheme and the error correction code according to the channel quality. For example, when the channel is good, the transmitter can use a higher order modulation (such as 16-QAM) and a lower code rate (such as 1/2) to achieve a higher data rate. When the channel is bad, the transmitter can use a lower order modulation (such as QPSK) and a higher code rate (such as 3/4) to improve the robustness and reliability of the signal.

4 How does GSM handle interference?

GSM stands for global system for mobile communications, which is based on frequency division multiple access (FDMA) and time division multiple access (TDMA). FDMA means that the frequency band is divided into narrow channels, and each user or service is assigned a specific channel. TDMA means that each channel is further divided into time slots, and each user or service is assigned a specific slot. This way, GSM can avoid interference by separating the signals in frequency and time domains.

5 How does GSM handle fading?

GSM does not use AMC, but it uses other techniques to mitigate fading. One of them is frequency hopping, which means that the transmitter and the receiver switch between different channels in a predefined pattern. This reduces the impact of frequency-selective fading, which occurs when some frequencies are more affected than others by multipath propagation. Another technique is diversity, which means that the transmitter or the receiver uses multiple antennas or paths to send or receive the same signal. This reduces the impact of spatial fading, which occurs when the signal strength varies depending on the location or orientation of the antennas.

6 How do WCDMA and GSM compare?

WCDMA and GSM have different advantages and disadvantages in dealing with interference and fading. WCDMA can achieve higher spectral efficiency, data rates, and capacity than GSM, but it requires more complex signal processing and synchronization. WCDMA can also adapt to the varying channel conditions better than GSM, but it is more susceptible to inter-cell interference and power control errors. GSM can offer simpler and cheaper devices and networks than WCDMA, but it has lower spectral efficiency, data rates, and capacity. GSM can also avoid intra-cell interference better than WCDMA, but it is more vulnerable to frequency-selective fading and co-channel interference.

7 Here’s what else to consider

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