Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-07-29
2001-07-10
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S310000
Reexamination Certificate
active
06259686
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to cellular radio communication networks allowing communications at various bit rates.
The mechanism of multiple access of mobile stations in such a network is one of the key points in the design of the network.
The present invention relates more particularly to a time division multiple access (TDMA) method.
TDMA systems are used in a number of existing cellular networks, especially those constructed according to the GSM standards designed for essentially fixed communication bit rates. The third-generation mobile radio systems, such as UMTS (Universal Mobile Telecommunication System) will have to support a wide range of services, with bit rates varying from 8 kbit/s to 2 Mbit/s. TDMA systems comparable to those used in GSM have been proposed in order to offer these services and fulfil the objectives of UMTS whilst ensuring some degree of compatibility with the existing GSM infrastructures (see Tero Ojanpera et al, “Comparison of Multiple Access Schemes for UMTS”, Proc. of the VTC'97 Conference, Phoenix, May 1997, Vol. 2, pages 490-495).
These proposals generally consider a definition of the radio interface matched to the cellular environment (indoor, outdoor propagation, microcells, macrocells etc.), but not to the type of service to be supported. Thus, for a given cellular environment, it is proposed to use a single bandwidth, the construction of channels with different bit rates resulting only from the allocation of a variable number of elementary timeslots per signal frame. This approach prevents optimization of the spectral resources as a function of the service bit rate, the structure being suitable for one type of bit rate only.
European patent application 0 719 062 discloses a radio communication system in which the used frequency band is divided into “channels”, wherein each channel itself may be subdivided into a number of frequency “conduits”. In order to allocate radio resource to a certain communication or to a certain service, there is provided either a time splitting of the “conduit” (TDM scheme) or a logic splitting by means of codes (CDMA scheme).
Another time and frequency mapping of the available radio resources is disclosed in European patent application 0 680 168.
A primary object of the present invention is to define a TDMA radio interface structure suitable for supporting a wide range of service bit rates. Another object is that this structure be flexible to use by the operator of the cellular network. It is also desired that this structure be compatible with radio resource optimization mechanisms, such as dynamic channel allocation (DCA) and/or frequency hopping.
SUMMARY OF THE INVENTION
The invention thus proposes a method of multiple access in a cellular radio communication network, the network allowing communications at different bit rates, with signals transmitted in successive frames each divided into elementary timeslots which can be used for different communications, wherein a frequency band is allocated to communications between base stations of a group of cells and mobile stations. The allocated frequency band is subdivided into frequency blocks each having a block width equal to 2
M−1
×B
0
where B
0
is a predefined elementary spectral width and M an integer greater than 1 chosen as a function of a specified maximum communication bit rate for the group of cells. Each of the blocks is divided into a number 2
M−m(i)
of carriers of spectral width 2
m(i)−1
×B
0
, m(i) being an integer dependent on the relevant block such that 1≦m(i)≦M and representing a type of carrier. The apportioning of the blocks and of the carriers within the allocated frequency band is identical for all the cells of the group. In order to support a communication in one of the cells, a logic channel is selected, defined, depending on the bit rate of said communication, as one or more elementary timeslots on one of the carriers.
With each request for a logic channel for a given communication bit rate, the operator can then define the widths of carriers best suited to supporting the communication, and preferentially allocate logic channels on such carriers. In general, it will be judicious to favour the allocation on narrow carriers.
The group of cells to which the method is applied can correspond to a geographical zone covered by the network. Advantageously, it may also correspond to a layer of cells in a multicellular type of network. In a multicellular network, the same geographical zone is covered by several layers of cells, the various layers corresponding to cells of different sizes. The smallest cells, or “microcells” are provided for communications with mobiles travelling at low or zero speed, whilst the “macrocells” are rather provided for mobiles travelling rapidly and in order to relieve the traffic from the microcells. Within the framework of the method according to the invention, the relevant frequency band is advantageously that allocated to one of the layers of the network, the other layers possibly having a similar or different spectral splitting mechanism.
The multiband structure used leads to the allocated frequency band being sliced up into blocks each containing carriers of homogeneous width. This strategy makes it possible to group together the services with equivalent bit rate into the same part of the band, so as to facilitate the obtaining of resources for the services at high bit rate.
The widest carrier is chosen at the level of the access network as a function of the cellular environment and of the maximum service bit rate to be supported. Advantageously, this choice can be modified dynamically, for example according to the time of day as a function of the traffic statistics. The slicing of each block into carriers can also be modified dynamically, if the distribution of the bit rates required varies over a day, or according to the day of the week etc. For example, it is possible to imagine that the services with the highest bit rate, which are supported by the widest carriers, might be prohibited at times of maximum traffic.
The multiple access method according to the invention is entirely compatible with the allocating of multiple timeslots of one and the same frame for one and the same logic channel. It also permits the concatenating of consecutive elementary timeslots on the same carrier so as to form physical channels which afford a higher communication bit rate than the sum of the bit rates afforded individually by these consecutive elementary timeslots.
The method also makes it possible to utilize a DCA mechanism. The following steps are then executed for each cell of the group:
assigning a priority to each carrier/timeslot pair as a function of qualities observed during communications within saidcell; and
for each communication bit rate, selecting the logic channels on the basis of said priority values.
Preferably, the selecting of a logic channel then comprises the steps of:
obtaining an ordered list of configurations of logic channels capable of supporting the bit rate of the communication, each logic channel configuration being defined by a type of carrier and by at least one number of timeslots within the frames;
searching for an available logic channel having the first configuration of the list and fulfilling a specified priority condition; and
if the preceding search yields a logic channel, selecting such logic channel for the communication, otherwise repeating the search for the next configuration of logic channel in the list.
The operator has a wide choice for defining the ordered lists of configuration of logic channels for each value of communication bit rate. Typically, the list will be ordered in such a way as to favour the least wide types of carriers, and to favour the concatenating of consecutive timeslots for the types of carriers where such a concatenation is permitted.
Another advantageous embodiment of the method employs frequency hopping from carrier to carrier within each set of carriers of the same type. It is in particula
Acx Anne-Gäele
Blanc Patrick
France Telecom
Marshall O'Toole Gerstein Murray & Borun
Olms Douglas
Pizarro Ricardo M.
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