CN101800567A - Method for distributing forwarding time slot and selecting relay node in cooperative ultra-wide band - Google Patents
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Abstract
The invention discloses a method for distributing a forwarding time slot and selecting a relay node in a cooperative ultra-wide band, belongs to the field of communication, and solves the problem of high conflict probability of relaying and forwarding a signal at a receiving end by adopting the conventional algorithm in the cooperative ultra-wide band. The method of the invention comprises the following steps: firstly, receiving pilot signals sent by a source node by each relay node; secondly, calculating channel gains from the source node to k relay nodes; thirdly, fitting a channel gain curve which obeys normal distribution, and dividing the interval [mu-3sigma, mu+3sigma] of the gain channel curve into N small gain intervals with the same area; and finally, distributing and forwarding time slot according to the channel gain proportional relation among the N small gain intervals. The method of the invention further comprises the following steps for selecting the relay node: fifthly, determining the small gain interval where the channel gain of each relay node is positioned according to the third step; sixthly, receiving the signal, forwarded by the relay node, corresponding to a target node by the target node according to the fourth step, and calculating an error rate; and finally, selecting the relay node corresponding to a route of which the error rate is lowest as the relay node for forwarding a data information signal.
Description
Technical Field
The invention relates to a method for allocating forwarding time slots and selecting relay nodes in a cooperative ultra-wideband, belonging to the field of communication.
Background
In recent years, ultra-wideband technology has become one of the candidates for the future short-range wireless interconnection and wireless sensor network due to its advantages of low power spectral density, high multipath resolution, etc., and in order to avoid interference to the existing systems, the federal communications commission in the united states published "FirstReportandOrder" in 2002 regarding ultra-wideband technology, which has allowed commercial application of ultra-wideband technology and also has made strict limitations on effective omnidirectional radiation power (EIRP) of ultra-wideband transmitters in indoor and outdoor applications. The peak EIRP at the position of 3.1 GHz-10.6 GHz of the working frequency band of the ultra-wideband transmitter is-41.3 dBm/MHz, and the peak EIRP is very low, so that the signal power received by the ultra-wideband receiver is also very low, and the design difficulty of the ultra-wideband receiver is increased. In order to guarantee the quality of the received signal while reducing the complexity of the ultra-wideband receiver, the prior document proposes to introduce cooperative communication into the ultra-wideband system.
The basic idea of cooperative communication technology originates from the three-terminal relay channel, but since there are many technical difficulties in implementing relay, research on cooperative communication has entered the bottleneck in the early 80 s of the last century. In recent years, cooperative communication technology has received much attention from researchers again due to the introduction of a user cooperation model established in a diversity fashion under uplink conditions.
By introducing the cooperation technology into the ultra-wideband system, the quality of received signals can be improved by utilizing the cooperation technology, and meanwhile, the transmitting power of an ultra-wideband transmitter can be reduced, so that the standby time of nodes is prolonged. However, due to the complexity limitation of the ultra-wideband receiver and the long time slot spreading caused by the dense multipath characteristics of the ultra-wideband channel, it is difficult for the ultra-wideband receiver to implement effective diversity combining, so in a cooperative ultra-wideband system, only one relay node is generally selected, that is, only one effective relay route is established to implement relaying of a transmission signal. Because a plurality of possible relay nodes exist around each node, how to select an effective relay node becomes a problem to be solved, and the existing feedback type relay node selection method or the synchronous relay node selection method does not consider the special requirements of the ultra-wideband system on simplification, real-time performance and the like of the relay node selection method, so that the method is not suitable for being directly applied to a cooperative ultra-wideband system. The feedback type relay node selection method needs extra transmission energy to transmit feedback information, and even feedback information with a small number of bits consumes a large amount of node energy, so that the relay node selection method in the cooperative ultra-wideband system should be asynchronous and without feedback in order to meet the requirements of simplification, real-time performance and the like of the relay node selection method.
In the process of asynchronous routing, one of the most critical steps is that the relay node forwards the pilot signal sent by the source node. In order to avoid collision of signals forwarded by each relay node when reaching a destination node and cause mutual interference of a plurality of received signals, the forwarding time slots of the relay nodes must be effectively and reasonably allocated.
In the existing algorithm, one solution is to set the forwarding timeslot in a form inversely proportional to the channel gain, where the channel gain is calculated by the relay node from the channel gains of the two sublinks from the source node to the destination node, but this method is not reasonable because the channel gain does not fully reflect the quality of the actual link. The other scheme is a method for evaluating the channel quality by adopting the bit error rate, and the forwarding time slot is set to be in a form in direct proportion to the bit error rate.
Both of the above-described forwarding slot allocation schemes essentially establish a linear mapping between channel quality and time slot. For the dense multipath environment in which the indoor ultra-wideband is located, the channel gain is normally distributed in decibels. Therefore, the channel gain is often around the mean of the normal distribution, the forwarding time slots of the two relay nodes are separated by a short time interval, and when the time interval is smaller than the multipath time slot spread of the channel, the signals forwarded by the two relays interfere with each other at the destination node, so that the performance of the system is reduced. The relay forwarding signal has high collision probability at the receiving end.
Disclosure of Invention
The invention aims to solve the problem that the collision probability of a relay forwarding signal at a receiving end is high by adopting the existing algorithm in the cooperative ultra-wideband, and provides a method for allocating the forwarding time slot and selecting the relay node in the cooperative ultra-wideband.
The method for allocating the forwarding time slot in the cooperative ultra-wideband comprises the following steps:
step one, each relay node in a cooperative ultra-wideband receives a pilot signal sent by a source node;
step two, respectively acquiring channel gains from the source node to k relay nodes according to the pilot signals received in the step one
Wherein i =1,2,3 … … k, k ≤ 50;
step three, fitting a curve of the channel gain changing along with the probability density and complying with the normal distribution according to the k channel gains acquired in the step two, and enabling the curve to be stable]Division of gain intervalsN small gain intervals with equal areas are formed, wherein N is a natural number larger than k, and N is not less than 5000 and not less than 100;
and step four, allocating forwarding time slots according to the channel gain proportional relation of the N small gain intervals.
Based on the steps, the method for selecting the relay node in the cooperative ultra-wideband further comprises the following steps:
step five, determining a small gain interval in which the channel gain of each relay node is positioned according to the step three;
step six, the destination node receives the signals forwarded by the relay node corresponding to the destination node according to the forwarding time slots determined in the step four, and calculates the error rate when the signals corresponding to each time slot arrive;
and step seven, selecting the relay node corresponding to the route with the minimum error rate as the relay node for forwarding the data information signal, and notifying the source node and each relay node of the selection condition in a broadcasting manner.
The invention has the advantages that: the invention provides a method for allocating the forwarding time slot, which obviously reduces the collision probability of the relay forwarding signal at the receiving end.
Establishing a nonlinear corresponding scheme between the channel quality and the relay forwarding time slot, subdividing the interval near the mean value, and roughly dividing the interval far from the mean value, thereby ensuring that the probability of falling into each section of interval is the same, and ensuring that the time slot difference corresponding to two adjacent intervals is larger than the maximum time slot extension of the multipath channel.
The method can effectively ensure that the forwarding time slots corresponding to the channel gains near the mean value are effectively distinguished, reduce the collision probability of the relay forwarding signals at the receiving end, further quickly select an effective relay node to forward information and ensure the performance gain of the cooperative ultra-wideband system.
Drawings
Fig. 1 is a flowchart of a method for allocating forwarding time slots in cooperative ultra-wideband, fig. 2 is a method for selecting relay nodes in cooperative ultra-wideband, fig. 3 is a schematic diagram of a cooperative ultra-wideband system, fig. 4 is a channel gain distribution diagram, and fig. 5 is a schematic diagram of allocating nonlinear relay forwarding time slots.
Detailed Description
The first embodiment is as follows: the following describes the present embodiment with reference to fig. 1 and fig. 3 to fig. 5, and the method for allocating a forwarding timeslot in cooperative ultra wideband of the present embodiment includes the following steps:
step one, each relay node in a cooperative ultra-wideband receives a pilot signal sent by a source node;
step two, respectively acquiring channel gains from the source node to k relay nodes according to the pilot signals received in the step one
Wherein i =1,2,3 … … k, k ≤ 50;
the channel gainObtained according to the following formula:
in the formula:
is shown asiPulse signals received by a time slot;
is shown asiThe estimated value of noise is received by each time slot relay node;
step three, fitting a curve of the channel gain changing along with the probability density and complying with the normal distribution according to the k channel gains acquired in the step two, and enabling the curve to be stable
]The gain interval is divided into N small gain intervals with equal areas, wherein N is a natural number larger than k, and N is not less than 5000 and not less than 100;
the channel gain curve obeying normal distribution is a probability density function:
wherein,Xis the channel gain, in decibels,
And step four, allocating forwarding time slots according to the channel gain proportional relation of the N small gain intervals.
The pilot signal sent by the source node is forwarded to the destination node through the relay node, and an effective relay node is selected from the k relay nodes, wherein the important link is the allocation of a plurality of relay node forwarding time slots, and two relay node forwarding signals cannot exist in one time slot at the same time so as to avoid collision.
A channel gain curve of k channel gains following normal distribution is constructed as shown in fig. 4, where the abscissa is the channel gain in decibels and the ordinate is the probability density, and is expressed by formula (1).
According to the characteristics of normal distribution, channel gainXIn [ 2 ]
]The probability of [ d ] is 99.7%, and thus, here, approximation is regarded as [ 2 ]
]The gain of all channels is covered in the intervalXThe case (1). Will be curved]The gain interval is divided into N small gain intervals with equal areas, and the areas are probabilities. Make the channel gainXThe probability of falling into each small gain interval is equal, as shown in figure 5, giving a specific embodiment, k =50, N =200, i.e. [ 2 ]]Since the gain section is divided into 200 small gain sections having the same area, the curve is normally distributed, and therefore the length of the 200 small gain sections on the horizontal axis is nonlinear, and the section time slot near the mean value (the center of the normal distribution diagram) is short, and the section time slot far from the mean value is long. The channel gain of the 5 th relay node falls in the 1 st small gain interval, and the channel gain of the 2 nd small gain interval falls inThe channel gain of the 2 nd relay node is entered, the channel gain of the 7 th relay node falls in the 3 rd small gain interval, the channel gain of the 13 th relay node falls in the … … th small gain interval, because N is greater than k, there are some small gain intervals without the channel gain value of any relay node, in this embodiment, there are 150 small gain intervals without the channel gain of any relay node, N is set greater than k, and 5000 ≧ N ≧ 100 is to avoid the channel gains of two or more relay nodes in one small gain interval, so as to avoid collisions.
The forwarding time slots are allocated according to the channel gain proportional relationship of 200 small gain intervals, that is, the forwarding time slots are allocated to be in a nonlinear relationship, the proportional relationship is the channel gain proportional relationship of 200 small gain intervals shown in fig. 5, the interval time slot near the mean value (the center of the normal distribution diagram) is short, and the interval time slot far away from the mean value is long, so that the probability of falling into each section of small gain interval is ensured to be the same, and the time slot difference corresponding to two adjacent small gain intervals is larger than the maximum time slot extension of the multipath channel. The 1 st time slot forwards the signal of the 5 th relay node, the 2 nd time slot forwards the signal of the 2 nd relay node, the 3 rd time slot forwards the signal of the 7 th relay node, the 200 th time slot forwards the signal of the 13 th relay node, and the time slots which do not fall into the channel gain of any relay node are not forwarded and are in an idle state, namely 150 time slots are in the idle state.
In order to minimize the collision probability, the probability of each section of small gain interval is adjusted to be the same, a nonlinear relay forwarding time slot allocation method is adopted, and the method is designed and completed based on the following principle:
setting channel gainXThe probability of falling into the ith small gain interval isp i Then there are at least two probabilities of arriving in the same time slot in the k relay forwarding signalspComprises the following steps:
in order to solve for the minimum collision probability of the forwarded signals, each forwarded signal is dropped into the secondiProbability of small gain intervalp i Are considered variables and they satisfy a constraint that the sum is 1. Thereby, the probability is calculatedpThe minimum value problem of (2) can be summarized as a nonlinear programming problem with constraints, namely:
according to the optimization condition of Karush-Kuhn-Tucker in the nonlinear programming,
wherein,lis a constant;prepresented by formula (2). Order toSTo pairp i The partial derivative is 0, i.e.:
calculated from (5) to obtain
Then, based on the constraint condition, it can obtain
. At this time, the process of the present invention,
the minimization of the collision probability is achieved.
The second embodiment is as follows: the following describes the present embodiment with reference to fig. 2, and the method for selecting a relay node based on the method for allocating a forwarding timeslot in cooperative ultra wideband according to the first embodiment further includes the following steps:
step five, determining a small gain interval in which the channel gain of each relay node is positioned according to the step three;
step six, the destination node receives the signals forwarded by the relay node corresponding to the destination node according to the forwarding time slots determined in the step four, and calculates the error rate when the signals corresponding to each time slot arrive;
the bit error rate is obtained according to the following formula:
BER=Q（SNR）
wherein, the BER is the bit error rate,
SNR is the signal-to-noise ratio.
And step seven, selecting the relay node corresponding to the route with the minimum error rate as the relay node for forwarding the data information signal, and notifying the source node and each relay node of the selection condition in a broadcasting manner.
According to the time slot allocation method in the first embodiment, a signal is forwarded, and after the signal is received by a target node, a best relay node is selected as an effective relay node to forward the signal according to an error rate.
A device for implementing the method for allocating forwarding time slots and selecting relay nodes in cooperative ultra-wideband of the present invention is shown in figure 3,
1. at the transmitting end (i.e. source node) of the signal, the pilot sequence generated by the pilot sequence generator and the pulse generated by the pulse generator generate a transmitted pilot pulse through the pulse shaper;
2. each relay node performs pulse correlation on a locally generated pulse signal template and a received pilot frequency pulse;
3. each relay node calculates channel gain and demodulates the channel gain and records the received pilot frequency through a memory;
4. each relay node performs a probability equivalence distributor on the channel gain according to the result;
5. and each relay node obtains a forwarding time slot according to the result matching of the probability equivalence distributor.
6. Each relay node is controlled by a pilot frequency memory and a time slot distributor to generate corresponding forwarding pulses and send the forwarding pulses through an antenna;
7. the target end (namely the target node) correlates the signal received by each time slot with the local template pulse, calculates the channel gain of the relay channel corresponding to each time slot through the gain calculator, and calculates the error rate of each channel according to the channel gain by the error rate calculator;
8. and the destination terminal optimal value decision device selects a time slot corresponding to the relay channel with the minimum bit error rate, codes the selection result, and generates a pulse signal containing the selection result through a pulse generator to send.
Claims (5)
1. A method for allocating forwarding time slots in cooperative ultra-wideband, the method comprising the steps of:
step one, each relay node in a cooperative ultra-wideband receives a pilot signal sent by a source node;
step two, respectively acquiring channel gains from the source node to k relay nodes according to the pilot signals received in the step one
Wherein i =1,2,3 … … k, k ≤ 50;
step three, fitting a curve of the channel gain changing along with the probability density and complying with the normal distribution according to the k channel gains acquired in the step two, and enabling the curve to be stable
]The gain interval is divided into N small gain intervals with equal areas, wherein N is a natural number larger than k, and N is not less than 5000 and not less than 100;
and step four, allocating forwarding time slots according to the channel gain proportional relation of the N small gain intervals.
2. The method of claim 1, wherein the channel gain in step two is greater than the channel gain in the cooperative ultra-wideband systemThe following formula is used for estimation:
in the formula:
is shown asiPulse signals received by a time slot;
is shown asiA local template pulse signal of each time slot relay node;
3. The method according to claim 1, wherein the channel gain curve obeying normal distribution in step three is a probability density function:
wherein,Xis the channel gain, in decibels,
4. The method for selecting a relay node based on the method for allocating a forwarding time slot in a cooperative ultra-wideband of claim 1, further comprising the steps of:
step five, determining a small gain interval in which the channel gain of each relay node is positioned according to the step three;
step six, the destination node receives the signals forwarded by the relay node corresponding to the destination node according to the forwarding time slots determined in the step four, and calculates the error rate when the signals corresponding to each time slot arrive;
and step seven, selecting the relay node corresponding to the route with the minimum error rate as the relay node for forwarding the data information signal, and notifying the source node and each relay node of the selection condition in a broadcasting manner.
5. The method for selecting a relay node in cooperative ultra-wideband as claimed in claim 4, wherein the bit error rate in step six is obtained according to the following formula:
BER=Q（SNR）
wherein, the BER is the bit error rate,
SNR is the signal-to-noise ratio.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102111209A (en) * | 2011-03-24 | 2011-06-29 | 山东大学 | Narrow pulse-based relaying method for cooperative ultra wideband communication system |
| WO2013000171A1 (en) * | 2011-06-30 | 2013-01-03 | 北京邮电大学 | Method and device for controlling relay transmission based on non-reproduction relay mode |
| CN104660524A (en) * | 2013-11-25 | 2015-05-27 | 国家电网公司 | Channel access control method and system of power line communication network |
| CN105260467A (en) * | 2015-10-16 | 2016-01-20 | 中国联合网络通信集团有限公司 | Short message classification method and apparatus |
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| CN101061669A (en) * | 2002-01-22 | 2007-10-24 | 飞思卡尔半导体公司 | Method for transmitting isochronous and asynchronous data in a wireless network |
| CN101228726A (en) * | 2004-04-06 | 2008-07-23 | 德州仪器公司 | Versatile system for dual carrier transformation in orthogonal frequency division multiplexing |
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| CN101061669A (en) * | 2002-01-22 | 2007-10-24 | 飞思卡尔半导体公司 | Method for transmitting isochronous and asynchronous data in a wireless network |
| CN101228726A (en) * | 2004-04-06 | 2008-07-23 | 德州仪器公司 | Versatile system for dual carrier transformation in orthogonal frequency division multiplexing |
| WO2006109934A1 (en) * | 2005-03-28 | 2006-10-19 | Pantech Co., Ltd. | Multiple access digital communicating method in ultra-wideband radio access networks |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102111209A (en) * | 2011-03-24 | 2011-06-29 | 山东大学 | Narrow pulse-based relaying method for cooperative ultra wideband communication system |
| CN102111209B (en) * | 2011-03-24 | 2013-08-21 | 山东大学 | Narrow pulse-based relaying method for cooperative ultra wideband communication system |
| WO2013000171A1 (en) * | 2011-06-30 | 2013-01-03 | 北京邮电大学 | Method and device for controlling relay transmission based on non-reproduction relay mode |
| CN104660524A (en) * | 2013-11-25 | 2015-05-27 | 国家电网公司 | Channel access control method and system of power line communication network |
| WO2015074574A1 (en) * | 2013-11-25 | 2015-05-28 | 国家电网公司 | Power-line communication network channel access control method and system |
| CN105260467A (en) * | 2015-10-16 | 2016-01-20 | 中国联合网络通信集团有限公司 | Short message classification method and apparatus |
| CN105260467B (en) * | 2015-10-16 | 2018-10-19 | 中国联合网络通信集团有限公司 | A kind of SMS classified method and device |
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