In cellular wireless networks, it is crucial to deal with Mobile station (MS) handoff between cells so that they can maintain a consistent and QoS-guaranteed service. There are 4 basic types of handoff protocols; network-controlled handoff (NCHO), mobile-assisted handoff (MAHO), soft handoff (SHO), and mobile-controlled handoff (MCHO). From NCHO in order to MCHO, the control protocols often decentralize the decision making process, which help reduce handoff delays; however , meanwhile, the particular decentralization makes the measurement information offered to make a handoff decision also reduced. Next, we briefly introduce these types of four types of handoff mechanisms.
Network-controlled handoff
NCHO is a centralized handoff process, in which it is network that makes handoff decision based on measurements of the transmission quality of mobile station (MS) at a number of based stations (BS). Specifically, if the MS is assessed to have a weaker signal in its outdated cell, while a stronger transmission in a neighbouring cell, then a handoff decision could be made by the system to switch BS from the old cellular to the new cell. Such a kind of handoff in general takes 100-200 microsoft and produces a noticeable "interruption" in the conversation. However , overall postpone of such a type of handoff is in common in the range of 5-10 s. Hence, this type of handoff is not suitable to some rapid changing environment and a very dense of users due to the associated postpone. NCHO is used in the first-generation analogue systems such as AMPS.
Mobile-assisted handoff
MAHO distributes the handoff decision procedure. It is MS makes measurements, as well as the Mobile switch centre (MSC) can make decisions on handoff. Compared to NCHO, this mechanism has more distributed manage, thereby helping to improve the overall handoff delay, typically in the range of one s.
Soft handoff
SHO is often utilized in conjunction with MAHO. Rather than instantly terminating the connection between a MICROSOFT and a BS. In the course of handoff, a brand new connection is established first between the MICROSOFT and a new BS, while maintaining the old connection between the MS as well as the old station. Only after the brand new connection can stably transmit information, the old connection is released. Hence, SHO is a "make before break" mechanism. This mechanism helps ensure the particular service continuity, which is however in the cost of more capacity resource usage during the handoff (as two cable connections are established simultaneously).
Mobile-controlled handoff
In contrast to NCHO, it is MICROSOFT that totally control and create decisions on handoff in the MCHO approach. A MS keeps upon measuring signal strength from all of the surround base station (BS)s. When the MS find that there is a new BALONEY who has a stronger signal compared to that of an old BS, it may think about to handoff from the old BALONEY to the new BS given a particular signal threshold is reached. MCHO is the highest degree of handoff decentralization, thereby enabling it to have a very quickly handoff speed, typically on the purchase of 0. 1 s.
Summary
We have introduced four types of handoff mechanisms that are widely used in mobile wireless networks. From centralization in order to decentralization, network-controlled handoff (NCHO) displays the highest centralization with the network completely controlling and making decisions upon handoff, while mobile-controlled handoff (MCHO) gives full flexibility to MICROSOFT to allow it to make decisions upon handoff. As a result, decentralized handoff systems show advantages of very fast handoff acceleration, while centralized mechanisms generally consider much longer time. In modern mobile wireless networks, decentralized handoff systems are widely applied due to their great scalability and fast handoff rates of speed.
This article was contributed simply by http://www.ylesstech.com.
Comments
Post a Comment