Patent Application
20170245303
The present invention relates to methods for managing a communication network and to corresponding devices.
In communication networks, it is generally desirable to efficiently utilize transmission resources. For example, some cellular communication systems, such like GSM (Global System for Mobile Communications) provide a frequency reuse larger than one. This means that adjacent cells of the same network do not use the same frequency band, and therefore do not interfere with each other. However, cells sufficiently far away from each other may use the same frequency resources. This way, a moderate level of inter-cell interference is guaranteed, while at the same time allowing reuse of the frequency resources.
While usage of cellular networks increases, available transmission resources tend to become more and more scarce. Accordingly, cellular technologies like the LTE (Long Term Evolution) technology specified by 3GPP (3rd Generation Partnership Project) have been developed to operate under conditions of high interference. The LTE technology may utilize a number of techniques to cope with high interference levels. For instance multiple antenna techniques may be used to improve the effective SINR (Signal to Noise Ratio) by increasing signal diversity and utilizing receiver side interference mitigation capabilities. Further, link adaptation may be used to make the transmission robust towards interference. For the link adaptation, modulation and coding schemes (MCS) may be selected so as to guarantee a maximum block error probability (BLER) for a given SINR. When the SINR is low due to of interference, a robust MCS may be used for transmission. When SINR is high, a higher order MCS may be selected to obtain the largest possible data rate at a wanted BLER. The BLER is typically set to 10%, sometimes even larger. This means that certain transmissions cannot be decoded correctly at the receiver. For such cases, a HARQ (Hybrid Automatic Request) protocol may be used as an error-recovery mechanism. By means of a HARQ retransmission the originally transmitted signal can be recovered in a short delay.
The above-mentioned robustness with respect to interference enables reuse of the same time-frequency resources in adjacent cells of the same network. This is called a reuse of one. Studies show that the achieved system capacity with a reuse of one is much higher than with separate time-frequency resources in adjacent cells.
To further improve availability of transmission resources, usage of transmission resources from an unlicensed spectrum was suggested. In the LTE technology, it is possible to aggregate carriers from different frequency bands for the same UE (User Equipment). In a concept referred to as LA-LTE (Licensed-assisted access LTE), aggregation of a carrier from a licensed spectrum with a carrier from an unlicensed spectrum is considered.
For the operation of the carrier in the unlicensed spectrum, additional mechanisms may be provided to ensure fair coexistence with other systems that may transmit in the same unlicensed band. For example, nodes of an LA-LTE network may need to coexist well with nodes of a WiFi network utilizing the same carrier. Further, the nodes of an LA-LTE network may need to coexist with nodes of a different LA-LTE network utilizing the same carrier. In 3GPP contribution RWS-140025 “Co-existence considerations for LTE-U”, by Cisco Systems, 3GPP workshop on LTE in unlicensed spectrum, Jun. 13, 2014, Sophia Antipolis, France, it is suggested to utilize a random backoff during channel access for enabling fair resource sharing in the unlicensed spectrum.
The random backoff defines a time period which a node has to wait after sensing that a channel has become free, before transmitting on the channel. By means of the random backoff, it can be ensured that two or more nodes backing off do not start transmitting at the same time.
By utilizing a random backoff mechanism, collision between an LA-LTE network and another network utilizing the same carrier, e.g., a WiFi or other LA-LTE network, can be avoided. However, the usage of of the random backoff mechanism may also block possible usage of the carrier by certain nodes. For example, interfering transmissions of LA-LTE nodes of the same network may be possible due to the above-mentioned techniques of coping with high interference levels, but usage of the random backoff mechanism may result in such transmissions being prevented in the same way as other colliding usage of the carrier.
Accordingly, there is a need for techniques which allow for efficiently controlling transmission in a communication network in view of efficient usage of transmission resources.
According to an embodiment of the invention, a method of controlling transmission in a communication network is provided. According to the method, a communication device detects potentially colliding usage of transmission resources. Further, the communication device detects cease of the potentially colliding usage of the transmission resources. After expiry of a backoff time period starting when detecting the cease of the usage of the transmission resources, the communication device performs a transmission on the transmission resources. This transmission is performed synchronously with a further transmission on the transmission resources by at least one other communication device.
According to a further embodiment of the invention, a method of controlling transmission in a communication network is provided. According to the method, a node of the communication network provides control information to multiple communication devices. These communication devices perform transmissions on transmission resources after a backoff time period starting when detecting cease of potentially colliding usage of the transmission resources. The control information enables synchronization of the transmissions by the communication devices.
According to a further embodiment of the invention, a communication device is provided. The communication device comprises at least one interface for transmission on transmission resources. Further, the communication device comprises at least one processor. The at least one processor is configured to detect potentially colliding usage of the transmission resources and detect cease of the potentially colliding usage of the transmission resources. Further, the at least one processor is configured to, after expiry of a backoff time period starting when detecting the cease of the usage of the transmission resources, perform a transmission on the transmission resources synchronously with a further transmission on the communication transmission resources by at least one other communication device.
According to a further embodiment of the invention, a node for a communication network is provided. The node comprises an interface for controlling multiple communication devices. Further, the node comprises at least one processor. The at least one processor is configured to provide control information to the multiple communication devices. The multiple communication devices are configured to perform transmissions on transmission resources after a backoff time period starting when detecting cease of potentially colliding usage of the transmission resources. The control information enables synchronization of the transmissions by the multiple communication devices.
According to a further embodiment of the invention, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of a communication device. Execution of the program code causes the at least one processor to detect potentially colliding usage of transmission resources and detect cease of the potentially colliding usage of the transmission resources. Further, execution of the program code causes the at least one processor to, after expiry of a backoff time period starting when detecting the cease of the usage of the transmission resources, perform a transmission on the transmission resources synchronously with a further transmission on the communication transmission resources by at least one other communication device.
According to a further embodiment of the invention, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of a node of a communication network. Execution of the program code causes the at least one processor to provide control information to multiple communication devices. The multiple communication devices are configured to perform transmissions on transmission resources after a backoff time period starting when detecting cease of potentially colliding usage of the transmission resources. The control information enables synchronization of the transmissions by the multiple communication devices.
Details of such embodiments and further embodiments will be apparent from the following detailed description of embodiments.
In the following, concepts according to embodiments of the invention will be explained in more detail by referring to the accompanying drawings. The illustrated concepts relate to control of transmissions in a communication network. Specifically, the concepts relate to efficiently controlling avoidance of colliding usage of transmission resources. The communication network may for example be based on one or more radio technologies, e.g., a cellular radio technology such as the LTE technology. If the communication network is based on a radio technology, the transmission resources may be frequency resources, such as one or more carriers. Although the examples explained in the following refer to a cellular network based on the LTE technology, it is to be understood that the illustrated concepts could be also applied in connection with other communication technologies, e.g., other cellular radio technologies, such as UMTS (Universal Mobile Telecommunications System) technology, or a WiFi radio technology, or even wire-based technologies.
In some scenarios, these different networks may each correspond to an LA-LTE network. Within each of these LA-LTE networks, mutual interference among nodes of the LA-LTE network is considered to be tolerable. However, between nodes of different LA-LTE networks, interference is considered to be not tolerable. In other scenarios, the different networks may be based on different radio technologies. For example, network A could correspond to an LA-LTE network, while network B corresponds to a WiFi network.
In the concepts as illustrated in the following, it is assumed that a CSMA (Carrier Sense Multiple Access) based mechanism is applied for avoiding colliding usage of the transmission resources by multiple communication devices. The CSMA based mechanism involves that a communication device 10, 100-1, 100-2, 100-3, 100-4 detects whether there is potentially colliding usage of the transmission resources, i.e., whether the transmission resources are free or not. For example, this detection may involve measuring an energy level on a carrier of the transmission resources. If the sensed energy level is below a certain threshold, the transmission resources may be regarded as free, and the communication device 10, 100-1, 100-2, 100-3, 100-4 may proceed by performing a transmission on the transmission resources. If the energy level is above the threshold, this is regarded as indicating a potentially colliding usage of the transmission resources, and the communication device 10, 100-1, 100-2, 100-3, 100-4 defers a transmission on the transmission resources, but waits until cease of the potentially colliding usage is detected. The communication device 10, 100-1, 100-2, 100-3, 100-4 then further waits for at least a backoff time period before performing the transmission on the transmission resources. In this way, colliding usage of the transmission resources may be avoided. In addition, for some of the communication devices 10, 100-1, 100-2, 100-3, 100-4, performing the transmission after the backoff time period in a synchronous manner is allowed. In particular, those communication devices 10, 100-1, 100-2, 100-3, 100-4 for which mutual interference is tolerable are controlled to synchronously perform the transmission after the backoff time period. For example, in the scenario illustrated in
For managing the synchronous transmissions, the communication devices 10, 100-1, 100-2, 100-3, 100-4 may be assigned to the above-mentioned different subnetworks, e.g., to network A and network B as illustrated in
The assignment of the communication devices 10, 100-1, 100-2, 100-3, 100-4 to the different subnetworks may be indicated implicitly, e.g., in terms of a network identity or node identity, such as a SSID (Service Set Identity), a BSSID (Basic Service Set Identity), or the like. Alternatively or in addition, the assignment may be indicated explicitly to the communication devices 10, 100-1, 100-2, 100-3, 100-4, e.g., in terms of dedicated identifiers of the subnetworks.
In the following, mechanisms for enabling the synchronization within one of the subnetworks, e.g., network A, will be explained in more detail.
In some scenarios, the backoff time period applied by the communication device 10, 100-1, 100-2, 100-3, 100-4 may be determined on the basis of a pseudo-random value. In such cases, the synchronization may be achieved by coordinating generation of the backoff time period applied by each of the communication devices 10, 100-1, 100-2, 100-3, 100-4 in such a way that the communication devices 10, 100-1, 100-2, 100-3, 100-4 of the same subnetwork will apply the same backoff time period while the communication devices 10, 100-1, 100-2, 100-3, 100-4 from different subnetworks will apply different backoff time periods which are randomly determined. The latter randomness may help to avoid that concerning the access to the transmission resources the communication devices 10, 100-1, 100-2, 100-3, 100-4 of one subnetwork are favored over the communication devices 10, 100-1, 100-2, 100-3, 100-4 from the other subnetwork. A corresponding exemplary scenario is illustrated in
The scenario of
In order to ensure that the AP1 and AP2 (and also AP3 and AP4) apply the same pseudo-random backoff time period TR, a centralized control node, such as the control node 200, could provide the pseudo-random backoff time periods to the different communication devices. For example, the control node 200 could generate the pseudo-random backoff time period TR applied by AP1 and AP2, while another control node (not illustrated) could generate the pseudo-random backoff time period TR applied by AP3 and AP4. In some cases, it is also possible that the same control node provides AP1 and AP2 with the same pseudo-random backoff time period TR, and provides AP3 and AP4 with another pseudo-random backoff time period TR.
Further, it can be utilized that typical algorithms for generating a random value produce a sequence of values which appears random, but in fact depends on an initial value of the algorithm, referred to as seed. The values not being perfectly random is reflected by the term “pseudo-random”. Accordingly, AP1 and AP2 may be provided with the same pseudo-random backoff time period TR by utilizing the same algorithm and seed for generating the pseudo-random backoff time period TR. The same algorithm, but a different seed may be utilized by AP3 and AP4. The coordination of the pseudo-random backoff time period TR for the different subnetworks may thus be achieved by configuring the communication devices of one subgroup with the same seed while configuring the communication devices of different subgroups with different seeds. This configuration could be accomplished by a centralized control node, such as the control node 200. For example, the control node 200 could provide the AP1 and AP2 with the same seed, while another control node (not illustrated) could provide AP3 and AP4 with another seed. In some cases, it is also possible that the same control node provides AP1 and AP2 with the same seed, and AP3 and AP4 with another seed.
In the above scenarios, various ways may be utilized to convey control information indicating the pseudo-random backoff time period TR or the seed to the communication devices. For example, such information could be broadcast to the communication devices of the same subnetwork. Further, the control information could be included in dedicated messages to each communication device.
In some scenarios, utilizing the same seed and algorithm in the communication devices of the same subnetwork may not be sufficient. For example, AP1 and AP2 may have originally used the same seed, but the transmission of AP2 may have been deferred due to the transmission of another communication device, which was not detected by AP1. This may cause AP2 to newly generate the pseudo-random backoff time period TR, while AP1 continues with the original pseudo-random backoff time period TR. Thus AP1 and AP2 would determine the pseudo-random backoff time period TR from the same pseudo-random sequence, but from different positions of the sequence. This may be addressed by regularly updating the seed of the algorithm to achieve the same state for each communication device of the subnetwork. A corresponding example of generating the pseudo-random backoff time period TR is illustrated in
In the example of
In some scenarios, coordination of the pseudo-random backoff time period TR may be also be achieved in a distributed manner by transmission of control information between the communication devices. This control information may allow for obtaining the same pseudo-random backoff time period TR for communication devices of the same subnetwork, while obtaining different pseudo-random backoff time periods TR fro communication devices of different subnetworks.
As illustrated in the exemplary scenario of
A more detailed process may be as follows: When one of the communication devices, e.g., AP1, selects the transmission resources for utilization, it may first monitor the transmission resources to check whether the transmission resources are already utilized by other communication devices, such as AP2, AP3, or AP4. If the communication device detects utilization of the transmission resources by one or more other communication devices from the same subnetwork, such as by AP2, it may adopt the state of the algorithm indicated by the other communication device for its own algorithm for pseudo-random generation of the backoff time period TR. Accordingly, the states of the algorithms for pseudo-random generation of the backoff time period TR will be coordinated to be the same for communication devices from the same subnetwork, e.g., for AP1 and AP2. If the communication device detects no utilization of the transmission resources by communication devices of the same subnetwork, it may select a local input to set the state of its algorithm for pseudo-random generation of the backoff time period TR. By way of example, such local input may be the current time, the network ID, the node ID, a serial number of the communication device, or a random number. Further, if the communication device detects utilization of the transmission resources by communication devices of another subnetwork, such as AP3 or AP4, the communication device may set the state of its algorithm for pseudo-random generation of the backoff time period TR to be different from that indicated in the preamble transmitted by the other communication device. This may ensure that communication devices of different subnetworks apply different pseudo-random backoff time periods TR.
A UE associated with an access node of one of the subnetworks, such as the UE 10, may obtain the state of the algorithm for pseudo-random generation of the backoff time period TR from this access node. The UE may also transmit the state of its algorithm for pseudo-random generation of the backoff time period TR in a preamble before it transmits data on the transmission resources and in this way indicate its network ID and the current state of the algorithm. The UE may be instructed by its serving access node to transmit such preamble in a periodic manner or on a one-time basis, e.g., via a physical layer command or higher layer signaling such as in an RRC (Radio Resource Control) command. The access node may select UEs that are farther away from the access node for such preamble transmission. The access node can determine the distance to the UE based various kinds of metric, e.g., based on timing advance measurements and/or transmission power level measurements.
In alternative scenarios, the pseudo-random generation of the backoff time period TR may be accomplished independently by each communication device, i.e., without coordination of the applied backoff time periods TR, and control information indicating a time instance of an upcoming transmission may be utilized for achieving the synchronization of the transmissions by the communication devices of the same subnetwork. A corresponding exemplary scenario is illustrated in
The scenario of
In the scenario of
The scenario of
As illustrated, in addition to sending the TX notification, AP1 also sends a CTS notification. The CTS notification may be sent immediately after or immediately before the TX notification. As explained in connection with
In other scenarios, the TX notification may be sent shortly before the upcoming transmission of data, with a time interval between sending the TX transmission being longer than the sensing time TS. A corresponding exemplary scenario is illustrated in
At step 710, the communication device may receive control information. Further, the communication device may also send control information. As further explained below, the control information may have the purpose of enabling synchronization of transmissions by the communication device with further transmissions by at least one other communication device.
At step 720, the communication device detects potentially colliding usage of transmission resources. The transmission resources may for example correspond to one or more carriers, e.g., from an unlicensed frequency band. The colliding usage may for example be detected by measuring an energy level on the transmission resources and comparing the measured energy level to a threshold. Such measurement may be performed over a certain time window, e.g., corresponding to the above-mentioned sensing time TS.
At step 730, the communication device detects cease of the potentially colliding usage of the transmission resources. Again, this may involve measuring an energy level on the transmission resources and comparing the measured energy level to the threshold, and the measurement may be performed over the same time window as mentioned in connection with step 710.
At step 740, the communication device waits at least for a backoff time period starting when detecting the cease of the usage of the transmission resources at step 730. The backoff time period may be determined by the communication device on the basis of a pseudo-random value. Alternatively, the backoff time period could be indicated to the communication device, e.g., by a control node such as the control node 200.
At step 750, the communication device performs a transmission on the transmission resources synchronously with a further transmission on the transmission resources by the at least one other communication device. For this purpose, the communication device may utilize the control information sent or received at step 710.
In some scenarios, the communication device may receive the control information from the at least one other communication device. For example, the control information may then include a seed for pseudo-random determination of the backoff time period as utilized by the at least one other communication device, e.g., as explained in connection with the distributed scenario of
In some scenarios, the communication device may also receive the control information from a node which is responsible for controlling the communication device and the at least one further communication device, such as from the control node 200. For example, the control information may then include a seed for pseudo-random determination of the backoff time period. To enable the synchronization, the node may provide the same seed to both the communication and to the further communication device. An example of corresponding processes is as explained in connection with the centralized scenario of
In both the centralized scenario and the distributed scenario, the seed for pseudo-random determination of the backoff time period may be based on a network ID and/or a current time. Further, the communication device may update the seed on a regular basis, e.g., on the basis of newly received control information or by sending new control information.
When the control information indicates a time instance of the transmission by the at least one further communication device, a time interval between receipt of the control information by the communication device and the transmission by the communication device may be larger than a sensing time for detecting usage of the transmission resources, such as explained connection with the scenarios of
At step 810, the node may control the communication devices. This may for example involve sending various kinds of control information to the communication devices.
At step 820, the node determines control information for synchronizing transmissions by the multiple communication devices. The control information may include a seed for pseudo-random determination of the backoff time period. To enable the synchronization, the node may provide the same seed to both the communication and to the further communication device. An example of corresponding processes is as explained in connection with the centralized scenario of
The seed for pseudo-random determination of the backoff time period may be based on a network ID and/or a current time. Further, the node may update the seed on a regular basis, e.g., by determining and sending new control information.
At step 830, the node sends the control information to the communication devices. For example, this may be accomplished by broadcasting the control information to the communication devices or by sending a dedicated message to each of the communication devices.
It should be noted that the steps of the methods of
As illustrated, the communication device may include a transmission interface 910 for performing transmissions in the communication network. For example, the transmission interface 910 may correspond to a radio interface, e.g., on the basis of a cellular radio technology, such as the LTE technology. Further, the communication device may include a control interface 920. The control interface 920 may for example have the purpose allowing remote control or configuration of the communication device.
Further, the communication device includes one or more processor(s) 950 coupled to the interfaces 910, 920 and a memory 960 coupled to the processor(s) 950. The memory 960 may include a read-only memory (ROM), e.g., a flash ROM, a random access memory (RAM), e.g., a dynamic RAM (DRAM) or static RAM (SRAM), a mass storage, e.g., a hard disk or solid state disk, or the like. The memory 960 includes suitably configured program code modules to be executed by the processor(s) 950 so as to implement the above-described functionalities of the communication device, e.g., as illustrated by the method of
It is to be understood that the structures as illustrated in
As illustrated, the control node may include a control interface 1010. The control interface 1010 may have the purpose controlling or configuring multiple communication devices of a communication network.
Further, the communication device includes one or more processor(s) 1050 coupled to the interface 1010 and a memory 1060 coupled to the processor(s) 1050. The memory 1060 may include a ROM, e.g., a flash ROM, a RAM, e.g., a DRAM or SRAM, a mass storage, e.g., a hard disk or solid state disk, or the like. The memory 1060 includes suitably configured program code modules to be executed by the processor(s) 1050 so as to implement the above-described functionalities of the control node, e.g., as illustrated by the method of
It is to be understood that the structures as illustrated in
As can be seen, the concepts as described above may be used for efficiently avoiding undesired collisions on certain transmission resources while at the same time allowing efficient reuse of the transmission resources.
It is to be understood that the examples and embodiments as explained above are merely illustrative and susceptible to various modifications. For example, the concepts may be applied in various kinds of communication networks, without limitation to the illustrated example of a cellular network or radio networks. For example, the concepts could also be applied to various kinds of wire-based communication networks. Moreover, it is to be understood that the above concepts may be implemented by using correspondingly designed software to be executed by one or more processors of an existing device, or by using dedicated hardware.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/067691 | 8/19/2014 | WO | 00 |
