How can multiple access techniques enable cooperative and cognitive wireless communications and networking?

1 Cooperative wireless communications

Cooperative wireless communications is a technique that allows wireless devices to help each other in transmitting and receiving data, by forming clusters or relays. This can increase the coverage, reliability, and diversity of wireless links, especially in scenarios with fading, shadowing, or interference. Multiple access techniques can facilitate cooperative wireless communications, by enabling different devices to coordinate their transmissions, exchange information, and allocate resources. For example, code division multiple access (CDMA) can allow multiple devices to use the same frequency band with different codes, while orthogonal frequency division multiple access (OFDMA) can assign different subcarriers to different devices according to their channel conditions.

2 Cognitive wireless communications

Cognitive wireless communications is a technique that allows wireless devices to sense and adapt to the spectrum environment, by using artificial intelligence, machine learning, or other methods. This can enable dynamic and opportunistic access to the spectrum, especially in scenarios with licensed and unlicensed users, or heterogeneous networks. Multiple access techniques can enable cognitive wireless communications, by allowing different devices to communicate and negotiate their spectrum access, avoid or mitigate interference, and optimize their performance. For example, non-orthogonal multiple access (NOMA) can allow multiple devices to use the same frequency band with different power levels or codes, while cognitive radio multiple access (CRMA) can allow different devices to switch between different frequency bands or channels according to their spectrum availability and quality.

3 Challenges and opportunities of multiple access techniques

Multiple access techniques are not without challenges and limitations, such as complexity, overhead, synchronization, fairness, security, and compatibility. Therefore, they require careful design, optimization, and implementation, taking into account the specific characteristics and requirements of cooperative and cognitive wireless communications and networking. However, multiple access techniques also offer many opportunities and benefits, such as flexibility, scalability, robustness, efficiency, and diversity. Therefore, they can play a key role in enabling and enhancing cooperative and cognitive wireless communications and networking, which are expected to revolutionize the future of wireless systems and applications.