Dynamic radio link adaptation

Details Dynamic radio link adaptation Dynamic radio link adaptation

1999-03-05

2003-02-04

Vincent, David (Department: 2732)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S464000

Reexamination Certificate

active

06515972

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio link protocols and more particularly to a dynamic data link adaptation for a wireless communication system.
2. Background Information
Layering, or layered architecture is a form of hierarchical modularity that is central to data network design. A layer performs a category of functions or services. All major emerging communication technologies rest on the layers. of the OSI model, illustrated in
FIG. 1-
a.
The OSI model defines a physical layer (Layer
1
) which specifies the standards for the transmission medium, a data link layer (Layer
2
), a network Layer
3
and application layers (layers
4
to
7
).
Physical Layer. The function of the physical layer is to provide a physical pipe, i.e. a communication link for transmitting a sequence of bits between any pair of network elements joined by a physical communication channel. E.g. in the case of wireless networks, this is the channel that physically transports the information between the mobile station (MS) and the base transmission station (BTS), or between the BTS and the mobile switch center (MSC).
Link Layer. Each point-to-point communication link has data link control modules at each end of the link. The purpose of these modules is to exchange information elements (IE), using the physical layer.
Link protocols are a recognized mechanism used within the wired and wireless communications industries to mitigate the effects of impairments introduced by the physical transmission medium. A radio link protocol (RLP) is one that is designed for the wireless environment to deal specifically with the types of impairments found on the radio link between a mobile station (MS) and the radio access network (RAN). The detailed mechanisms employed by an RLP are usually specific to a particular air interface protocol (AIP) and are tailored to the services supported by that AIP. In general, a link protocol may provide mechanisms to deal with errors on the communications link, delays encountered in transmitting information over the communications link, information lost while transmitting over the communications link, bandwidth conservation and contention resolution.
All these AIPs define a limited number of RLPs and select the RLP for a connection during the connection setup phase based on the service requirements. The service is defined by the type of information (ToI) transmitted (i.e. voice, packet data, control packet, etc.) and by the quality of service (QoS) required. Generally speaking, the quality of service (QoS) of a particular type of service (ToS) is dependent upon the errors encountered over the communication link, the delays encountered in transmitting the information, and/or the information lost while transmitting over the communications link.
As discussed above, a radio link protocol may provide mechanisms to deal with all type of impairments introduced in the radio link by the physical transmission medium. Thus, error control schemes are currently designed for error detection only, error detection and forward error correction, or error detection and retransmission. Current delay control schemes include expedited delivery, bounded delay or unbounded delay, while loss control schemes may include assured delivery, best-effort delivery, or relay service (no recovery). Current bandwidth conservation schemes may include packet header compression, generic payload compression, or application specific compression, and contention resolution schemes may include randomized backoff interval followed by retransmission, channel reservation, round-robin or priority-based polling or adaptive power stepping followed by retransmission. This list of protocol functions is by no means exhaustive.
Network Layer. The third layer is the network layer which is responsible for routing packets from one network node to another. The network layer takes upper layer data units (packets), adds routing information to the packet header, and passes the packet to the link layer.
Transport Layer. The fourth layer is the transport layer which creates virtual end-to-end connections using network layer addressing and routing capabilities. This layer has a number of functions, not all of which are necessarily required in any given network. In general, this layer is concerned with assembling/reassembling of data units, multiplexing/demultiplexing, end-to-end error correction, flow control, etc.
The Transmission Control Protocol (TCP) shown in
FIG. 1
b
as the transport layer, has evolved over many years of use in the wired local area network (LAN) and wide area network (WAN) arenas. However, many of the algorithms used to optimize the performance of TCP in the wired environment are based on some underlying assumptions about the wired network where the TCP is typically used.
Wired and Wireless Environment
In a wired network the bit errors rates are typically on the order of 10
−9
or better, and bit errors have a tendency to be random. In general, the transmission medium is considered essentially error-free and TCP packets are lost mainly due to congestion in the intervening routers. Moreover, in a wired system the transmission channel has a constant bandwidth and is symmetrical; therefore, the characteristics of the channel in one direction can be deduced by looking at the characteristics of the channel in the other direction.
Due to the practically error-free environment of the wired networks, it is often easiest to use a common link control protocol and to solve congestion problems by “throwing bandwidth at the problem”, to remove queuing bottlenecks by using higher speed transmission channels.
On the other hand, in a wireless environment, most of the above assumptions are no longer valid. The wireless channel is characterized by a high bit error rate with errors occurring in bursts that can affect a number of packets. Due to fading, due to the low transmission power available to the mobile station and to the effects of interference, the bandwidth of the channel appears to rapidly fluctuate over time resulting in a radio link that is not symmetrical.
In a wireless environment, the amount of bandwidth available to the system is fixed and scarce. Adding bandwidth on the radio link may be expensive or even impossible due to regulatory constraints.
For example, optimizing bulk file transfer in a wired environment is simply a matter of allocating as much bandwidth as possible to the connection. In a wireless environment, part of the bandwidth is used in error correction. It is known that more error correction means less payload, however, more error correction increases the probability of correct delivery without retransmissions. Thus, end-to-end throughput may actually be increased by reducing bandwidth assigned to payload and using the freed bandwidth for error correction.
Wireless network solutions targeted specifically at packet data using the Transmission Control Protocol (TCP) have been proposed but they suffer from a number of problems as they are generic to TCP with no distinction made between the requirements of the different applications that use TCP, and with no knowledge of the capabilities provided by different link and application layer protocols.
Another problem associated with the use of the TCP in a wireless network relates to a link layer which works independently of the TCP layer with no intrinsic knowledge of the control and information packet requirements of TCP. The link layer protocol may use mechanisms e.g. automatic retransmissions of lost or corrupted packets, that either duplicate or interfere with mechanisms used by TCP.
Priority-based queuing algorithms as well as parameter controlled behavior for use by RLPs have been also proposed. Priority-based queuing algorithms for use by RLPs are limited in their applicability to problems that can be solved with different queuing algorithms. Parameter controlled behavior as a means to modify the behavior of an RLP according to the values assigned to input parameters, is limited by initial decisions

Affiliated with

Also associated with

Rating

Dynamic radio link adaptation does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dynamic radio link adaptation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic radio link adaptation will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3128676