JP3404206B2 - Slot allocation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to slot allocation in a wireless communication system adopting a time division multiple access (TDMA) communication system, and more particularly to a slot allocation method in a system in which single slot and multi-slot allocation are mixed. .

[0002]

2. Description of the Related Art The prior art will be described with reference to FIGS. 7, 8, 9, and 10. FIG. 7 is a diagram for explaining a TDMA communication system of 8 slots / 1 frame which is a frame structure of a personal handyphone system (PHS), and FIG. 8 is frequency division multiplexing in 3 slots / 1 frame which is a frame structure of digital cellular. TDMA that adopts (FDD)
FIG. 9 is an explanatory diagram of a communication system, FIG. 9 is a diagram showing an example in which several channels are already in use in a TDMA communication system adopting time division multiplexing (TDD) with an 8 slot / 1 frame structure, and FIG. 10 shows 3 Slot / one frame TDMA
It is a figure which shows the example in which several channels are already in use by a communication system.

In FIG. 7, reference numeral 1 represents one frame. The frame consists of several slots. A slot indicates a predetermined communication time, that is, a schedule, between a certain terminal and a base station. For example, terminal A is previously given a slot (time schedule) in which communication is possible for each transmission and reception such that terminal A transmits to the base station using slot 1 and receives from the base station using slot 5. Allocating an appropriate slot according to a communication slot allocation request is called slot allocation.

Current TDs such as digital cellular and PHS
In the MA communication system infrastructure, one set of slots for uplink / downlink is allocated, and there is no system that uses a plurality of slots in one terminal. However, expectations for a communication system that uses multiple slots have risen from the standpoint of multimedia support, and the '94 Autumn College of Science B2
No. 60 describes a control channel configuration method when two slots are used in PHS, and '93 Spring Univ. B430, describes voice / non-voice simultaneous transmission based on PHS. .

The slot configuration of PHS and digital cellular will be described in more detail. Each standard is PH
S to RCR-STD28, digital cellular to RCR
-STD 27. FIG. 7 shows the PHS slot configuration. One frame consists of 8 slots, the front 4
The slots are uplink and the latter four slots are downlink.

Consider a case where slot allocation is performed by PHS in the example shown in FIG. In the example, the number of carriers is 7. In the figure, the thick framed slots indicate slots that are already in use and cannot be assigned due to new call generation. P
HS is a TDD system, and the right 4 slots and the left 4 slots are paired for each carrier. Therefore, the vacant slots can be described only by the four slots on the right side or the left side, and 17 slots are vacant in the example of FIG. If a request for allocation of 2 slots occurs, 4 × 13 + 5 × 8 + 2 × 6 = 104 combinations of allocations are possible. However, if two continuous and different frequency slots are assigned, such as No. 1 and No. 4, the resonance frequency of the frequency modulation synthesizer must be switched and stabilized within the guard time, resulting in low cost and miniaturization. It is difficult to deal with the required mobile terminals.

Therefore, in the prior art, for example, JP-A-6-77886.
This problem is solved by a method of allocating two slots of the same frequency as shown in Japanese Patent Publication No.
In this case, in the slot use state of FIG. 9, only 14 allocation methods are possible.

On the other hand, FIG. 8 shows the slot structure of the digital cellular. Cellular is an FDD system, and the uplink frequency f1 and the downlink frequency f2 use different frequency bands. Consider a case where slot allocation is performed by cellular in the example shown in FIG. In the example, the number of carriers is 7. In the figure, the thick framed slots indicate slots that are already in use and cannot be assigned due to new call generation. In the example, 13 slots are vacant. When a request for allocation of 2 slots occurs, 5 × 8 + 5 × 3 = 55 combinations are possible. Also in this case, if two slots within the same frequency are to be allocated, the number of combinations is drastically reduced, and only seven allocation methods are possible. When a plurality of slots are allocated on the same frequency in this way, if a small number of slots are allocated at random, a frequency having a plurality of empty slots will disappear at an early stage.

[0009]

As described in the prior art, when a request for allocation of a plurality of slots is issued,
Allocating multiple slots to the same frequency is convenient for terminal miniaturization and cost reduction. Therefore, it is necessary to perform slot allocation so that a plurality of slots remain in the same frequency as much as possible.

Further, when the same communication device uses a plurality of consecutive slots in TDMA communication, the preamble part is not necessary in the second and subsequent slots. If data is transmitted instead, the overhead can be reduced. Therefore, it is necessary to perform slot allocation so that a plurality of consecutive slots remain.

[0011]

[Means for Solving the Problems] The above problem is that the time division multiple access communication system is adopted, and when allocating a communication slot between a terminal and a base station, one slot is included in one frame for communication with a small communication capacity. , And 1 for communication with a large communication capacity
In a communication system characterized by being able to deal with communication of various communication capacities by allocating multiple slots in a frame, the slot usage status investigated by the latest carrier sense in the past and the counting result of counting the number of empty slots for each frequency are shown. Step 1 in which the frequency is recorded in the accumulating means and a frequency having a vacancy of N slots or more and the smallest counting result is searched from the counting result;
In the frequency searched in step 2, a slot that is vacant in the slot usage situation is set as an allocation candidate slot, and carrier sense of the allocation candidate slot determined in step 2 is performed, and the carrier recorded in the storage means is recorded. Step 3 of updating the slot usage status and the counting result
If, as a result of the carrier sense in step 3, the allocation candidate slot is empty, the communication channel is allocated to the slot and the slot use status and the counting result recorded in the storage means are updated, and step 4 in step 3 As a result of the carrier sense, if the allocation candidate slot is not empty, the control is transferred to step 5, and as a result of searching in step 1, if there is no frequency having an allocatable slot, the terminal is denied allocation. It can be solved by allocating the slot of the communication channel according to the flow including the notification step 6.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention is shown in FIGS.
This will be described with reference to FIGS. 7 and 9. 1 is a diagram showing a flow of slot allocation according to an embodiment of the present invention, FIG. 2 is a view showing a reference table when performing slot allocation by applying the embodiment of the present invention, and FIG. 7 is a PHS frame. FIG. 9 is a diagram showing the configuration, and FIG. 9 is a diagram showing an example in which there are slots in use in the PHS.

In FIG. 7, reference numeral 1 indicates a frame. One frame consists of 8 slots. Slots 1 to 4
Is used for the uplink and slots 5-8 are used for the downlink. FIG. 9 shows an example of a situation in which it is actually used.
In the example, with 7 carriers configuration, upstream 4 × 7 = 28 slots,
Downlink 28 slots are prepared. The thick framed slots indicate slots in use, and 19 slots are currently empty. In the following, a case will be described as an example where only one slot or two slots are requested to be allocated in one frame.

In the example of FIG. 9, when a slot allocation request for 2 slots is generated, 104 slot allocations are possible. However, when randomly allocating slots, for example, allocating numbers 1 and 4,
Since two different frequencies are used in consecutive slots, the resonance frequency of the synthesizer required for down-converting from RF to baseband and up-converting from baseband to RF must be switched at high speed. If the switching operation does not fall within the guard time, the first half of the slot will be crushed and correct demodulation will not be possible.

The following method can be given as a countermeasure. That is, (1) two synthesizers that improve the performance of the synthesizer are used alternately. Since both of these two methods lead to price increase, they can be implemented in the base station, but it is difficult to implement in terminals that require severe price. Therefore, as another solution, a method of allocating two slots of the same frequency can be considered. Since frequency switching does not occur in this method, no special hardware is required in the terminal, and it can be realized at a low price. However, this method has a new problem that the number of assignable combinations is drastically reduced. In the example of FIG. 9, the number of combinations of allocation is 14 ways, which is reduced to about 1/8.

A decrease in the number of combinations of allocations leads to an increase in the probability of allocation failure, that is, a call loss rate, resulting in a reduction in system capacity. Further, if slots are randomly allocated, a plurality of empty slots on the same frequency may disappear in an early stage, and a request for allocation of a plurality of slots may result in a call loss.

When allocating one slot, no matter which vacant slot candidate is allocated, since there are as many combinations as there are vacant slot candidates, it does not matter which vacant slot is allocated. There 1
When allocating slots, if the slots are allocated so that a plurality of slots remain in the same frequency as much as possible, the number of combinations when allocating two slots can be increased. As a result, the call loss rate can be reduced and the problem can be solved.

Since the PHS has an 8-slot TDD configuration, 4 slots on one side are the basis of the frame. When all 4 slots are unused, there are 6 possible combinations for assigning 2 slots. Similarly, there are three cases when three slots are unused and one case when two slots are unused. In this way, the combination of 2-slot allocation increases in a factorial manner according to the number of empty slots in the same frequency. Therefore, in the 1-slot allocation, the combination of 2-slot allocation will not be significantly reduced if the frequencies are allocated from the fewest empty slots.
Therefore, the problem is solved.

The flow of allocation will be described with reference to FIG.
In the following, a slot that has been vacant in the past carrier sense will be referred to as an estimated vacant slot, and a slot from which an estimated vacant slot is selected and to which a communication channel is to be allocated will be referred to as an allocation candidate slot. The reason for using this notation is that there is an elapsed time from the latest carrier sense in the past until the actual slot allocation, and during that time, another communication device may use the slot and the allocation may fail. This is to clarify that there is.

In step 1, a reference table showing a slot use state as shown in FIG. 2 is created from the latest carrier sense investigation. In the attribute, a count result is recorded as to how many slots are available at the same frequency. The value of this attribute indicates the priority of frequencies. For example, in the case of a 1-slot allocation request, the frequency having the smallest attribute of 1 or more is the highest priority.

In step 1, the highest-priority frequency search is performed, and the process proceeds to step 2. In the example of FIG. 2, f7 having an attribute of 1 is output as a search result.

Next, in step 2, the allocation candidate slot is determined from the frequency (f7) searched in the previous step 1. If there are multiple estimated empty slots, a random number is used for selection. In the example of FIG. 2, since f7 has an estimated empty slot only for s1, s1 is selected in this step.

In step 3, the carrier sense of the allocation candidate slot is performed to judge whether the allocation candidate slot is empty. Also, the reference table is updated based on the result of carrier sense.

In step 4, as a result of the carrier sense in step 3, if it is confirmed that the allocation candidate slot is unused, the communication channel slot allocation is performed. Also, since the slot usage state changes due to this slot allocation, the reference table is updated and the allocation operation is terminated.

As a result of the carrier sense in step 3, if the allocation candidate slot is in use, the process proceeds to step 1 (step 5). In the example of FIG. 2, when it is found that s1 is being used for carrier sense, the process proceeds to step 1, and the priority, that is, f3 or f5, which has the second smallest attribute, 2, is selected as a random number. Select by. After that, the process proceeds to step 2 and the allocation candidate slot is determined. In step 1, all the frequencies having an attribute of 1 or more in the table of FIG. 2 are searched, and if there is no frequency in which an allocatable slot exists, a refusal of allocation is transmitted to the terminal (step 6), and the process ends.

By this series of processing, the decrease in the number of allocatable slots when a two-slot allocation request occurs can be minimized. Therefore, the problem is solved.

In the present embodiment, the case where a request for allocating one slot or two slots occurs has been described as an example.
Even when a plurality of slots are assigned, the effect of the present invention does not change. By avoiding allocation to a frequency having a large number of estimated empty slots in allocation of a small number of slots, it is possible to reduce the call loss rate when a large number of slot allocations occur.

Another embodiment of the present invention will be described with reference to FIG. This embodiment shows an example of selecting allocation candidate slots.

In the above-described embodiment, the method of selecting the allocation slot candidates from the plurality of empty slot candidates in the same frequency in step 2 is random selection using random numbers. However, when talking to the same terminal,
2 if it is possible to allocate multiple consecutive slots
Since the preamble portion is unnecessary in the slots after the th slot, the overhead can be reduced. In this embodiment, a method for preventing selection of a frequency having a large number of empty slots on the same frequency when allocating consecutive N slots will be described.

The flow of the allocation method of this embodiment is the same as in FIG. The difference is how to assign attributes, and an example is shown in FIG. In FIG. 3, an example is shown in which 3 carriers are prepared in an 8-slot 1-frame configuration. f1 is s1,
s4 is in use and there are 2 consecutive empty slots
There are consecutive slots and four consecutive slots. The attribute describes the number of consecutive empty slots and the number of consecutive empty slots.

Therefore, in f1, the columns of the attributes 2 and 4 are set to 1 and it is shown that there are one 2 consecutive slots and one 4 consecutive slots. Next, in f2, s1 and s
3 and s6 are in use, and the number of slots that are continuously vacant is one for one slot and two for two consecutive slots, and this is indicated in the attribute. As for f3, only s5 is in use and 3 consecutive slots and 4 consecutive slots are vacant.

Consider a case where an allocation request for three consecutive slots occurs in this state. The priority of frequencies is the frequency with 3 or more consecutive slots and the smallest consecutive slot, and f
3 is the first priority and is an allocation candidate. If carrier sense is performed for 3 slots starting from s6 of f3 and it is revealed that allocation cannot be performed, allocation is attempted to 4 consecutive slots starting from s1 of f3. 4 in succession
There are two methods of allocating 3 consecutive slots to the vacant slots, but in this embodiment, allocation candidate slots are randomly determined. When it is found that the allocation candidate slot is in use in any case due to carrier sense and cannot be allocated, the frequency is changed and s of f1 is changed.
Select an allocation candidate from 4 slots starting from 5.
Further, even if f1 is assigned due to carrier sense, the assignment is rejected and the call is lost. This series of allocation methods attempts to allocate as long as possible a continuous long free slot, and the problem is solved.

Another embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a diagram showing a flow of a slot allocation method according to an embodiment of the present invention, and FIG. 5 is a view showing a reference table when performing slot allocation by applying the embodiment of the present invention.

In this embodiment, a case where a 4-slot allocation request occurs will be described as an example. In the embodiment shown in FIG. 1, the method of selecting the allocation slot candidate from the plurality of empty slot candidates in the same frequency in step 2 is random selection using random numbers. However,
When making a call with the same terminal, if a plurality of consecutive slots can be assigned, the preamble part is not required in the second and subsequent slots, and thus the overhead can be reduced. To this end, it is necessary to allocate slots so that continuous slots are not destroyed as much as possible when a request for allocation of a small number of slots occurs. Therefore, in this embodiment, a method of leaving a large number of consecutive large slots as much as possible when allocating a small number of non-consecutive slots is shown.

FIG. 4 shows a flow of the allocation method. Figure 1
The difference from the embodiment of FIG. In step 13 which replaces step 1, the highest priority frequency is determined from the attributes of the reference table as shown in FIG. Four
If a slot allocation request occurs, the number of empty slots with consecutive attributes is added in ascending order, and when the total number reaches the maximum value of less than 4 of the allocated slots, it is still added. Select the frequency that has the remaining non-existing empty slots and has the smallest minimum consecutive number of the remaining bright slots.

In the example of FIG. 5, since f1 is 1 + 5 slots, the minimum continuous number is 5, since f2 is 1 + 5 slots, the minimum continuous number is 5, and since f3 is 1 + 1 + 2 slots, the minimum continuous number is 2, and f4 is only 4 slots. The number is four. Therefore, the first priority frequency is f3.

Next, in step 14, when selecting the allocation slot, the estimated empty slots estimated to be empty are found from the reference table shown in FIG. 5, and the consecutive slots are prioritized in the order of the smallest number of consecutive estimated empty slots, and the consecutive slots are consecutive. For each estimated empty slot in the slot, one of the front and back is in use or an allocation candidate slot.
Touches and is either the beginning or the end of the frame
Estimated empty slot, occupied or allocation candidate slot
Higher priority is given to the estimated empty slot sandwiched between the frames, the estimated empty slot that is either the beginning or the end of the frame, and the estimated empty slot that is in use before or after one of the estimated empty slots. From the slot, N pieces are set as allocation candidate slots.

To give a specific priority to each slot, for example, one of the front side and the rear side is in use or assigned.
Touches the complementary slot and does not start or end the frame
If it is an estimated empty slot that is a gap 1, it is in use or
Is an estimated empty slot between allocation candidate slots
Mule 2, if the estimated free slot is either the beginning or end of a frame 3, if the estimated free slot, which is one before and after use or during allocation candidate slot 4
Value is added to the slot, and the value obtained by adding 5 times the number of consecutive estimated empty slots to which the slot belongs to as a priority, and N pieces are assigned in order from the smallest priority. Slots.

In the example of FIG. 5, f3 is s1, s3, s7, s
8 is an empty slot, but the priority of each is 7,
6, 14, 13 are assigned candidate slots in the order of s3, s1, s8, and s7 (step 14).

In step 15, carrier sense is carried out to update the reference table. As a result of the carrier sense in step 15, if it is found that the allocation candidate slot is already in use, control is transferred to step 13. With this series of flows, the assignment candidate slots are determined so as not to collapse the longest possible continuous slots, so that the problem is solved.

Another embodiment will be described with reference to FIG. Figure 6
FIG. 9 is a diagram showing a reference table when the present invention is applied to perform slot allocation.

In the embodiment shown in FIG. 4, a method of allocating non-consecutive minority slots so as not to collapse consecutive slots as much as possible was described. In this embodiment, the case where the minority slot to be assigned is also a continuous slot will be described. This eliminates the need for the preamble part in the second and subsequent slots for the communication for which the allocation request has been generated, and thus the overhead can be reduced. Further, since the continuous large number of slots are allocated so as not to be crushed as much as possible, it is possible to reduce the call loss rate when a large number of continuous slot allocation requests occur thereafter.

The flow of the allocation method of this embodiment is the same as in FIG. The difference is how to assign attributes and how to assign priority when deciding allocation candidate slots. An example of the reference table is shown in FIG. 6, and the method of assigning attributes is the same as the method of continuous slot allocation shown in FIG. The frequency to be assigned is determined from this attribute. For example, when allocating N consecutive slots, the frequency having the smallest number of consecutive slots of N or more is given the highest priority. When there are a plurality of frequencies with the highest priority, all frequencies with a plurality are targeted. The priority of the allocation candidate slots is N consecutive estimated empty slots sandwiched between the used slots, N consecutive estimated empty slots that are in use before and after one of the slots and include either the beginning or the end of the frame, N, including either the beginning or the end slot
It is assumed that consecutive estimated empty slots and N consecutive estimated empty slots, one of which is in use before and after, are in order.

This is compared with all N consecutive slots included in all frequencies having the highest priority, and the N consecutive slots having the highest priority are set as allocation candidate slots. As a result, slots can be assigned so as not to collapse a large number of consecutive slots.

FIG. 6 shows an example of allocation. In the figure, one frame consists of 8 slots and consists of 4 carriers. If there is a request for allocation of 3 slots, f4 having a continuous empty slot of 4 slots is the highest priority frequency from the attribute. In f4, 4 of s4, s5, s6, s7
The method of allocating three consecutive slots that have no slots is s4, s5, s6 and s5, s6.
There are only 3 slots of s7. Since both of these two have the same slot priority, one of them is randomly selected as an allocation candidate slot. If it is found by carrier sense that the allocation candidate slot is already in use, for example, if s5 is found to be in use, the reference table is updated and the frequency of the highest priority is determined again. Run.

Although the embodiment has been described by taking the PHS as an example, the effect of the present invention does not change in a system including the digital cellular system and adopting the TDMA communication system.

[0047]

As described above, according to the present invention, it is possible to allocate a small number of slots without crushing the allocation combination of a large number of slots, and it is possible to reduce the call loss rate when a large number of slots are allocated.

[Brief description of drawings]

FIG. 1 is a flow chart of slot allocation according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a reference table when slot allocation is performed by applying the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a reference table when performing slot allocation by applying the embodiment of the present invention.

FIG. 4 is a flowchart of an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a reference table when performing slot allocation by applying the embodiment of the present invention.

FIG. 6 is an explanatory diagram of a reference table when slot assignment is performed by applying the embodiment of the present invention.

FIG. 7 is an explanatory diagram of a PHS slot configuration.

FIG. 8 is an explanatory diagram of a slot structure of digital cellular.

FIG. 9 is an explanatory diagram showing an example in which some slots are already in use in the PHS slot configuration.

FIG. 10 shows a digital cellular slot configuration.
Explanatory drawing which shows the example in which some slots are already in use.

[Explanation of symbols]

1 ... frame.

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 7/24-7 / 26,102 H04Q 7/00-7/38

Claims (2)

(57) [Claims] 1. When a time division multiple access communication system is adopted and a communication slot between a terminal and a base station is allocated, one slot in one frame is used for communication with a small communication capacity, and communication with a large communication capacity is performed. In a communication system capable of coping with communication of various communication capacities by allocating a plurality of slots in one frame, the means for accumulating the slot use status investigated by the latest carrier sense in the past and the number of empty slots for each frequency are accumulated. And record it in
A first step of searching for a frequency with the smallest count result having N slots or more from the counting result, and an arbitrary slot that is empty in the slot usage condition within the frequency searched in the first step a second step of the candidate slots, wherein the third step that the carrier sense performing real second allocation candidate slots determined in step, the third step of the carrier sense result, the long allocation candidate slot empty a fourth step intends line call channel allocated to the slots, the third step of the carrier sense result, allocation candidate slot is not empty, a fifth step of transferring control to the first step, in the first step As a result of searching,
A slot allocation method, characterized in that when there is no frequency having an allocatable slot, a speech channel slot allocation is carried out in the flow of the sixth step of notifying the terminal of allocation refusal. 2. The number of slots continuously vacant on the same frequency as the slot use status investigated by the latest carrier sense in the past is recorded in the accumulating means, and N counts are recorded. In the case of allocating the consecutive slots of the above, the seventh step of assigning a high priority to each frequency from the counting result in the order of the number of consecutive empty slots being N or more and decreasing and searching the frequency having the highest priority, An eighth step in which an arbitrary slot estimated to be empty from the slot usage status within the frequency searched in the seventh step is set as an allocation candidate slot;
A ninth step that the carrier sense of fixed allocation candidate slot subjected real in step, the ninth step of the carrier sense result, intends row call channel assigned to that slot if allocation candidate slots empty 10th
If the allocation candidate slot is not empty as a result of the carrier sense in the step and the ninth step, the seventh step is performed.
As a result of performing the 11th step of transferring control to the step, and the 12th step of notifying the terminal of the allocation refusal when there is no frequency having the allocatable slot as a result of the search in the 7th step Slot allocation method for slot allocation.