CDMA: Advantages and Disadvantages

This page explores the advantages and disadvantages of the CDMA (Code Division Multiple Access) technique. It highlights both the benefits and drawbacks of CDMA. You’ll also find links to various resources covering CDMA basics.

What is CDMA?

Introduction: CDMA stands for Code Division Multiple Access. It’s a cellular technology composed of two primary systems:

• Base Station (BS)
• Mobile subscribers or users

Unique codes are assigned to each user, enabling communication with the Base Station (BS) or NodeB. CDMA allows multiple transmitters to simultaneously transmit information over a single channel, allowing multiple users to share the same bandwidth.

In CDMA, users utilize the entire bandwidth at all times. Each user has a unique code (e.g., PN codes) to recover their data. The system is based on the spread spectrum concept.

Benefits or Advantages of CDMA

Here are the key benefits and advantages of CDMA:

• Robustness: CDMA is resistant to fading and noisy environments because the signal is spread across a wide bandwidth during transmission.

• Security: The transmitted information exists below the noise floor, making it difficult to intercept the CDMA spectrum. Deciphering the CDMA code used over the traffic channel is also a challenge for hackers, making CDMA a more secure system.

• Capacity: CDMA allows the use of the entire bandwidth simultaneously. Unlike TDMA and FDMA, there’s no hard limit on the number of subscribers per cell. The limit depends on the number of codes supported by the CDMA-compliant base station. Adding users is relatively easy.

• Soft Handoff: During handovers between cells, CDMA utilizes a soft handoff feature. A connection is established with the new cell before disconnecting from the old one, minimizing the chances of dropped calls or disconnections.

• Interoperability: CDMA networks can interoperate with other cellular networks such as GSM/LTE, allowing nationwide roaming without issues.

Drawbacks or Disadvantages of CDMA

Here are the key drawbacks and disadvantages of CDMA:

• Orthogonality Requirement: CDMA uses orthogonal codes for mobile subscribers. Maintaining orthogonality between these codes is crucial for data recovery. Subscribers farthest from the Base Station (BS) experience greater attenuation, which can disrupt orthogonality and make data recovery difficult.

• Complex Handoff: CDMA utilizes soft handoff, which involves establishing a connection with the new target cell before disconnecting from the serving cell. This process is more complex than hard handoff techniques.

• Code Synchronization: Precise code synchronization is necessary to recover the original baseband signal.

• QoS Degradation: As the number of users increases, the overall Quality of Service (QoS) can decrease.

• Near-Far Problem: CDMA systems encounter the near-far problem. This requires careful control of the transmit power of CDMA handsets. The CDMA phone farthest from the BS must transmit at a higher power compared to a closer phone to maintain a good Signal-to-Noise Ratio (SNR) at the Base Station.

• Self-Jamming: Self-jamming can occur in CDMA systems due to the loss of orthogonality in PN codes or spreading sequences of different subscribers.