Random access method for NB-IOT devices

Abstract

Invention is a method for a system comprising plurality of NB-IoT devices (200) and at least a NB-IoT base station (100) for serving said NB-IoT devices (200), performing a random access procedure. It is characterized by comprising steps of: broadcasting transmission parameters comprising a success backoff time by said NB-IoT base station (100), and comprising following steps realized by NB-IoT device (200); receiving transmission parameters, transmitting a random access preamble to NB-IoT base station (100), if it is determined that random access is successful after transmitting said random access preamble, transmitting another random access preamble to NB-IoT base station (100) after said success backoff time.

Description

[0001] DESCRIPTION

[0002] RANDOM ACCESS METHOD FOR NB-IOT DEVICES

[0003] TECHNICAL FIELD

[0004] Invention relates to a method for a system comprising plurality of Narrow Band Internet of Things (NB-loT) devices and at least a NB-loT base station for serving said NB-loT devices, performing a random access procedure and a system thereof.

[0005] PRIOR ART

[0006] Narrow Band Internet of Things (NB-loT) is a low power wide area network (LPWAN) technology standard developed by 3rd Generation Partnership Project (3GPP) for cellular network devices and services. It has been in development since 3GPP Release 13, in which narrowband 1 (NB1 ) was introduced. In Releases 16 and 17, NB-loT Enhanced is introduced with power / latency reduction and higher modulation rates.

[0007] NB-loT devices (in general loT devices) are characterized by low data transmission rates, low power consumption, and low bandwidth. A typical application scenario is machine-type communications (MTC), where large data volumes are generated by small data packets, so many MTC devices require channel access simultaneously, which causes collision and a decrease in network performance. Hence, coordinating MTC devices is crucial to optimize network performance regarding access delay and throughput. In NB-loT networks, one possible solution is to optimize the back-off period, which is explicitly stated in 3GPP standards (3GPP TS 36.300. “Overall description.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E- UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN). httos: / / www.3aDD.ora).

[0008] NB-loT devices may access to NB-loT base station by random access procedure. Random access procedure may be contention based or contention free.

[0009] Contention-based random access which is initiated by users during initial access requires a four-step handshake. Four-step handshake starts with NB-loT devices sending a randomaccess preamble, randomly chosen by NB-loT devices from available preambles which are broadcasted during downlink synchronization, the second step of the connection establishment phase of the NB-loT communication process. Then, in the second step, the base station broadcasts a random-access response, which announces the successfully detected preambles without collision. NB-loT devices whose preambles are successfully detected, continue to third and fourth steps to establish RRC connection. Available preambles are limited, so a limited number of NB-loT devices may successfully access to NB-loT base station.

[0010] If an NB-loT device has data to send, it sends random access preamble to the NB-loT base station with attempt probability (p). If the random-access preamble transmission fails, NB-loT devices wait for some duration, which is predetermined by the back-off period (Tbo) before performing retransmission.

[0011] EP3420777B1 discloses a method of performing a random access procedure includes randomly selecting a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit, waiting until a time initialized with the backoff time expires, and retransmitting a random access preamble.

[0012] Access delay can be defined as the time between two consecutive resource allocations to the same user. Alternatively, access delay is the time elapsed since the user last accessed channel resources. Access delay violation probability is the probability of the instantaneous access delay exceeding a predefined access delay threshold.

[0013] When network size increases some of the NB-loT devices may successfully access more often and some of the NB-loT devices may fail to access for long time. This situation increases the access delay violation probability experienced by NB-loT devices. Prior art disclosures do not mention or solve this problem.

[0014] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0015] BRIEF DESCRIPTION OF THE INVENTION

[0016] The present invention relates to method and system to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field. An objective of the invention is increasing the number of NB-loT devices served by an NB-loT base station while reducing NB-loT devices’ access delay violation probabilities.

[0017] To achieve all the objectives mentioned above and that will emerge from the following detailed description, the present invention relates to a method for a system comprising plurality of NB- loT devices and at least a NB-loT base station for serving said NB-loT devices, performing a random-access procedure. Accordingly it is characterized by comprising steps of:

[0018] - broadcasting transmission parameters comprising a success backoff time by said NB-loT base station, and comprising following steps realized by NB-loT device;

[0019] - receiving transmission parameters,

[0020] - transmitting a random access preamble,

[0021] - if it is determined that random access is successful after transmitting said random access preamble, transmitting another random access preamble after said success backoff time. This prevents a NB-loT device to consecutively successfully access and occupy the channel resources so that other devices have higher chances of successful access. Thus, number of NB-loT devices served by the NB-loT base station is increased and NB-loT devices’ access delay violation probabilities are reduced.

[0022] A possible embodiment of the invention is characterized in that said transmission parameters further comprising a failure backoff time, said method comprising following steps realized by NB-loT device:

[0023] - if it is determined that random access is failed after transmitting said random access preamble, transmitting another random access preamble after said failure backoff time.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a drawing illustrating schematic view of the system.

[0026] Figure 2 is a drawing illustrating schematic view of NB-loT device and NB-loT base station.

[0027] Figure 3 is a drawing illustrating communication between NB-loT device and NB-loT base station according to one embodiment of subject matter method. REFERENCE NUMBERS GIVEN IN THE FIGURE

[0028] 100 NB-loT base station

[0029] 110 Processing system

[0030] 120 Network size estimator

[0031] 130 Base station transceiver means

[0032] 200 NB-loT device

[0033] 210 Processing unit

[0034] 220 Device transceiver means

[0035] DETAILED DESCRIPTION OF THE INVENTION

[0036] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0037] Present invention is a method realized by a system for managing random-access procedure of NB-loT devices (200) to a NB-loT base station (100).

[0038] Referring to figure 1 , system comprises plurality of NB-loT devices (200) and at least a NB-loT base station (200).

[0039] Referring to figure 2, NB-loT device (200) comprises a device transceiver means (220) which transmits signals to NB-loT base station (100) and receives signals from NB-loT bases station (100). NB-loT device (200) comprises a processing unit (210) which is electrically connected to device transceiver means (220). Processing unit (210) may comprise a processor which may be a microprocessor, for executing instructions stored on a storage device. Processor unit (210) may be connected to data sources (such as a sensor) for receiving data to be transmitted to a NB-loT base station (100). NB-loT devices (200) are well known in the art. Further details are not disclosed herein.

[0040] NB-loT base station (100) is a base station that is compatible with NB-loT technology and capable of communicating NB-loT devices (200). NB-loT base station (100) may comprise a base station transceiver means (130) for transmitting signal to NB-loT devices (200) and receiving signal from NB-loT devices (200). NB-loT base station (100) comprises a processing system (210) connected to base station transceiver means (130). NB-loT base station (100) may be a terrestrial base station or non-terrestrial base station. In a possible embodiment NB- loT base station (100) may comprise a network size estimator (120) which estimates number of nodes in a network. Processing system (110) may comprise processors, storage units and other components that base stations comprise that are well known in the art.

[0041] NB-loT base station (100) broadcasts available random access preambles that is available. NB-loT devices (200) know available random-access preambles. NB-loT device (200) randomly selects a random-access preamble and requests random access from NB-loT base station (100) by transmitting selected random-access preamble if there is no access restriction. NB-loT base station (100) then accepts random access request if there is not random-access preamble collision with another NB-loT device (200). NB-loT base station (100) then transmits random access response to NB-loT device (200). NB-loT device (200) realizes scheduled transmission after receiving response from NB-loT base station (100). After NB-loT base station (100) receives scheduled transmission from NB-loT device (200), it transmits a contention resolution to NB-loT device (200). This is defined as a successful access. If random access preamble received from NB-loT device (200) has a collision with another NB-loT device (200), NB-loT base station (100) does not transmit random access response. NB-loT device (200) then determines this random-access attempt as failed access.

[0042] The subject matter method provides NB-loT devices (200) to wait after a successful access, thus preventing consecutive successful access events in consecutive possible time slots or close time slots from same NB-loT device (200). Thus, allowing other NB-loT devices (200) that has not successfully access to have higher chance of a successful random access.

[0043] The subject matter method comprises following steps realized by the system.

[0044] - NB-loT base station (100) broadcasts transmission parameters comprising a success backoff time. Success backoff time is a time window that a successfully accessed NB- loT device (200) must wait before another random-access attempt.

[0045] NB-loT device (200) receives transmission parameters.

[0046] - NB-loT device (200) transmits a random access preamble to NB-loT base station (100). If it is determined that random access is successful after transmitting said random access preamble, NB-loT device (200) transmits another random-access preamble to NB-loT base station (100) after said success backoff time. Referring to figure 3, in a possible embodiment

[0047] - NB-loT base station (100) calculates success backoff time according to below formula: 1.92 where Tsb0is success backoff time, M is number of available preambles and N is network size.

[0048] N is determined by network size estimator. M may be predetermined.

[0049] In a possible embodiment, said transmission parameters further comprise an failure backoff time. The method further comprises following steps realized by NB-loT device (200):

[0050] - if it is determined that random access is failed after transmitting said random access preamble, transmitting another random-access preamble to NB-loT base station (100) after said failure backoff time.

[0051] - NB-loT base station (100) may calculate failure backoff time according to below formula:

[0052] Tba= 0.192 where Tb0is failure backoff time, M is number of available preambles and N is network size.

[0053] In another possible embodiment, in addition to success backoff time and failure backoff time transmission parameters may comprise attempt probability. Attempt probability is calculated using following formula;

[0054] / V p = -0.0082 X — + 0.425

[0055] M

[0056] NB-loT device (200) attempts random access based on received attempt probability.

[0057] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1 . A method for a system comprising plurality of NB-loT devices (200) and at least a NB- loT base station (100) for serving said NB-loT devices (200), performing a random access procedure, characterized in that comprising steps of:- broadcasting transmission parameters comprising a success backoff time by said NB-loT base station (100), and comprising following steps realized by NB-loT device (200);- receiving transmission parameters,- transmitting a random access preamble to NB-loT base station (100),- if it is determined that random access is successful after transmitting said random access preamble, transmitting another random-access preamble to NB-loT base station (100) after said success backoff time.

2. The method according to claim 1 , characterized in that said transmission parameters further comprising an failure backoff time, said method comprising following steps realized by NB-loT device (200):- if it is determined that random access is failed after transmitting said random access preamble, transmitting another random-access preamble to NB-loT base station (100) after said failure backoff time.

3. The method according to claim 1 , characterized in that NB-loT base station (100) calculating success backoff time according to below formula:Tsbo= 1.92where Tsb0is success backoff time, M is number of available preambles and N is network size.

4. The method according to claim 2, characterized in that NB-loT base station (100) calculating failure backoff time according to below formula:Tb()= 0.192where Tb0is failure backoff time, M is number of available preambles and N is network size.

5. A system comprising plurality of NB-loT devices (200) and at least a NB-loT base station (100) for serving said NB-loT devices (200) for performing a random-access procedure characterized in that said NB-loT base station (100) comprising a base station transceiver means (130) for broadcasting transmission parameters comprising a success backoff time; said NB-loT device (200) comprising a device transceiver (220) means for receiving transmission parameters and transmitting a random-access preamble to NB-loT base station (100), a processing unit (210) configured to transmit another random-access preamble to NB- loT base station (200) after said success backoff time if random access is successful after transmitting said random access preamble.

6. The system according to claim 5, characterized in that said transmission parameters further comprising an failure backoff time, said processing unit (210) is configured to transmit another random-access preamble to NB-loT base station (100) after said failure backoff time if it is determined that random access is failed after transmitting said random access preamble.

7. The system according to claim 5, characterized in that NB-loT base station (100) comprising a network size estimator (120) and a processing system (110) configured to calculate success backoff time according to below formula:where Tsb0is success backoff time, M is number of available preambles and N is network size.

8. The system according to claim 5, characterized in that NB-loT base station (100) comprising a network size estimator (120) and a processing system (110) configured to calculate failure backoff time according to below formula:NTbo= 0.192 x — M where Tb0is failure backoff time, M is number of available preambles and N is network size.

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