In wireless communication systems where channels are time-varying certain transmission parameters (e.g. data transmission rate, or transmission power) should be adapted to channel conditions in order to conduct a reliable communication. This is referred to as link adaptation in the wireless communication literature.  For example, modulation and coding rate can be to adjusted to adapt transmission rate according to the channel conditions.

+Resource allocation:

To enable a communication systems certain resources are necessary such as  power  and bandwidth. Resource allocation deals with efficient utilization of power and bandwidth to ensure better quality of service and performance . Indeed, this resource allocation  depends on channel conditions but also include the pricing in order to provide different type and quality of services for users.

Plead check my paper about "Resource Allocation in IEEE 802.16 e Mobile WiMAX Networks: Survey" 

In wireless communication systems depending on the application that the system is designed for we may have different QoS requirements and in each case a specific adaptation scheme should be performed in order to adapt the transmission to channel variations and provide a reliable communication. In general, we have two types of systems.

In the first type a maximum throughput is desired and system parameters (e.g. rate and power) are adapted according to channel conditions to maximize throughput. For example consider a system that has fixed transmission power, then the transmission rate is adapted according to the mutual information of the channel. In this case the transmission rate would be adaptive and is changing over time.This is what is usually called 'link adaptation' in the wireless literature. In order to perform link adaptation the users may also perform resource (e.g. power) allocation. For example, when the power and the rate can be adapted but there is an average power constraint the transmission power can be allocated over different time slots according to a water-filling approach to maximize mutual information and transmission rate can be adapted accordingly. So, link adaptation can be performed together with resource allocation.

The other type of the systems may desire a fixed-rate transmission (for example in voice communication or communication for control applications). Therefore, transmission powers can be adjusted in order to maintain mutual information of the channel at certain level higher than the desired transmission rate. Then, a reliable fixed-rate transmission would be possible. This requires a resource allocation problem to be solved.

In summary, depending on the QoS requirements and the underlying constraints in the system, terminals may perform link adaptation, resource allocation or a combination of these approach to satisfy the QoS requirements and maintain a reliable communication.

Hello Folks,

Link adaptation refers to modifying the wave form (transmit power, modulation scheme, packet length, carrier frequency, bandwidth, symbol rate, etc.) which is related to the connection with the communicating peer (s).  While, resource allocation refers to reserving the common resources (in the region) to specific node (s), such as carrier frequency (channel), storage, and other physical resources

I hope it becomes clear

Regards to all and Happy new year

Ali Mahdi