Product manual

System description, DECT air interface

Technical Product Manual - DCT1800-GAP

TD 92093 (1/LZBNB 103 108 R4D) / 2006-03-09/ Ver.C

Blind time slots

Usually a cordless phone has only one receiver circuit. So, when a cordless phone has an ongoing

call, it cannot monitor the same time slots of other carriers. In addition, it usually takes one time slot

to switch from one carrier frequency to another one. This means that the cordless phone neither can

monitor the time slot before and the time slot after the one in use. Time slots that cannot be monitored

are called blind slots. Dealing with blind slots is dependant upon the system.

Handover types

The change to another channel is referred to as a handover which can be seamless or not. A seamless

handover is not noticed by users - you do not hear any clicks or mutes. The principle of a seamless

handover is that the new channel is first seized in parallel to the old one, then the bit stream is

transferred to the new one, after which the old channel is released. Seamless handover is not a

requirement of DECT.

Fig. 24 Handover types

Handovers can be divided into intracell, intercell and external handovers (see figure 24). ‘Cell’ refers

to the radio coverage area of a base station. ‘Internal’ refers to handovers within a DECT system and

‘external’ refers to handovers between DECT systems. ’Intracell’ refers to handovers within a base

station and ’intercell’ refers to handovers between base stations belonging to the same DECT system.

For information on MAC and DLC layer, see paragraph 6.4.

Intracell handover

An intracell handover is a change to another channel of the same base station (see figure 25). It is

mainly used when the current channel is interfered by other DECT devices or any other sources

operating at the same frequency. A cordless phone also may request an intracell handover to see

base stations transmitting in its blind time slots.

Intracell handover is normally handled by the MAC layer (bearer handover). Bearer handovers do not

require the system’s CPU as the handover process takes place within the base station.

Intracell handovers can also be handled as a connection handover. In this case the selected (new)

base station will be the same as the ’old’ base station. In other words, implementing only one handover

algorithm (connection handover) in a cordless phone (saves memory) both intracell and intercell

handovers are supported. However connection handovers require processing time from the CPU.

Handover types

Internal External

(NWK layer)

IntercellIntracell

011

Bearer

(MAC layer)

Connection

(DLC layer)

Connection

(DLC layer)