Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-06-16
2004-09-14
Vuong, Quochien B. (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S445000, C455S443000, C370S331000
Reexamination Certificate
active
06792273
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reserving resources in a cellular radio communications system. One example and non-limiting application of the invention relates to advance reservation of data processing and memory resources needed to accommodate probable handover operations for a mobile radio connection.
BACKGROUND AND SUMMARY OF THE INVENTION
In a cellular radio communications system, a handover operation allows an established radio connection to continue when a mobile radio participating in that connection moves between cells in the system. Handover is typically initiated when the signal strength or signal quality of the radio connection with an origination base station falls below a predetermined threshold value. Often, a low signal strength or a poor signal quality indication means that the mobile station is near a border between two cells. If the mobile station moves closer to a destination cell or to a clearer line of unobstructed sight, handover of the radio connection to the destination cell usually results in improved radio transmission and reception.
In some cellular systems, a handover operation requires physically breaking the connection with the origination cell and then re-establishing the connection with the destination cell, i.e., a “break-before-make” switching operation. Such “hard” handover techniques are typically employed in Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) type cellular systems. On the other hand, “soft” handover techniques may be employed in Code Division Multiple Access (CDMA) type cellular systems. CDMA is an increasingly popular type of access for cellular communications because a higher spectrum efficiency is achieved compared to FDMA and TDMA techniques which means that more cellular users and/or services can be supported. In addition, a common frequency band allows simultaneous communication between a mobile station and more than one base station. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the mobile stations. Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately received at the receiving station. The high speed PN modulation also advantageously allows the receiving station to generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal.
In CDMA, therefore, a mobile station need not switch frequency when handover of a connection is made from one cell to another. As a result, a destination cell can support a connection to a mobile station at the same time the origination cell continues to service the connection. Since the mobile station is always communicating through at least one cell during handover, there is no disruption to the call. Hence the term—“soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
FIG. 1
is a high level diagram of a radio communications system
10
showing a soft handover operation. A radio network controller (RNC)
12
is coupled to adjacent base stations
14
and
18
. Base station
14
serves a cell area
16
, and base station
18
serves a cell area
20
. Mobile stations
22
and
24
are located within cell
16
, and mobile station
26
is located in cell area
20
. Because mobile station
24
is near the border between cells
16
and
20
, it has established communication links P
1
and P
2
with both base stations
14
and
18
which simultaneously support the connection with the mobile station
24
. When a mobile station is in soft handover between two base stations, a single signal is created at the mobile station receiver from the two signals transmitted by each base station using a RAKE demodulation combination process. Those two signals are generated by the RNC “splitting” or broadcasting a downlink signal intended for the mobile station into two parallel identical signals with one being directed to the origination base station
14
and the other to the destination base station
18
. In the opposite “uplink” direction, the mobile station transmitter broadcasts the signal to both base stations, and the signals are combined in the RNC
12
. More than two base stations may be involved in a soft handover.
A similar operation may occur between sector cells of a common base station that employs plural antennas. The radio communications system
10
in
FIG. 2
shows a base station
30
coupled to RNC
12
having multiple sectors Sec
0
-Sec
5
where each sector includes one or more sector antennas. Mobile station
32
is located on the border of sectors
0
and
1
. Demodulation elements at the base station
30
demodulate mobile station signals received at both sectors
0
and
1
. Combining the demodulated mobile station signals from sectors
0
and
1
at the base station permits “softer handover” to take place. In other words, the mobile connection is supported by a destination sector before an origination sector no longer supports the connection.
Accordingly, soft and softer handover are highly desirable features of a mobile radio communications system based on spread spectrum CDMA because they offer make-before-break switching of a connection and also because they offer diversity combining of plural paths of the same signal. Diversity combining combats fading and interference. However, system resources must be allocated in order to carry out handover operations. In soft handover, for example, diversity handover units (DHOs) located in the RNC perform macro diversity combining of the connection information in the uplink (mobile-to-base) direction and macro diversity splitting of the connection information in the downlink (base-to-mobile) direction. Moreover, a single DHO entity (an entity may be implemented using software and/or hardware) may be employed for each service provided to a mobile station, i.e., a call may include several services like voice, video, and data services in a multimedia call. Because the number of DHO entities required to support a connection varies depending on the call, it is considered a dynamic service parameter. Services may also specify at the time of request certain radio interface type parameters like a particular bandwidth, e.g., peak or average bit rate, or a particular delay, e.g., maximum tolerable delay. These types of parameters are considered static. Ultimately, software and hardware resources must be allocated to support both dynamic and static service parameters. At a basic resource level, data processing and memory resources are required to support service parameters associated with a call connection with the mobile station.
Higher level resources like CDMA spreading codes and lower level resources like data processing and memory can be allocated at the time of a call setup for a requested service or at the time a known service is added or removed from a call by matching those resources needed for the requested service(s). On the other hand, there are other unknown services or services that are not explicitly requested that nevertheless require hardware and software resources. For example, a number of handover paths ultimately used to support a mobile station connection is not specified or known at the time of call setup. Indeed, the number of handover paths will likely vary depending upon the mobile station's location and on the current radio conditions in the mobile communications network. A mobile station that is in the center of a particular cell will likely employ fewer handover paths, and therefore, fewer associated resources are needed to support those paths as compared to a mobile station traveling to or located near the border between two or more cells. A mobile station in this latter situation will likely require more resources to support plural handover pat
Engman Göran
Gustavsson Pär
Tellinger Jan
Wahlman Stefan
Lele Tanmay
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
Vuong Quochien B.
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