WO2013063789A1

WO2013063789A1 - Data communication methods and apparatus

Info

Publication number: WO2013063789A1
Application number: PCT/CN2011/081778
Authority: WO
Inventors: Chao Li; Shiping Duan; Yeping Xiao; Yu Wang
Original assignee: Beijing Weibang Yuanhang Wireless Technology Co., Ltd
Priority date: 2011-11-04
Filing date: 2011-11-04
Publication date: 2013-05-10

Abstract

A data communication method between a user equipment (UE) and a base station (BS). The BS is set to begin to transmit downlink data at regular time intervals T. The method comprises the UE beginning to transmit uplink access data packets to access the BS at transmission times which are determined with reference to distance information between the BS and the UE to compensate for delay time for data travelling between the BS and the UE. This method extends the data communication range to beyond 100 km to facilitate the deployment of more efficient and long-range mobile data communication systems, such as air-to-ground data communications systems or data communication system for high-speed trains.

Description

DATA COMMUNICATION METHODS AND APPARATUS

Filed of the Invention

The present invention relates to data communication methods and apparatus, and more particularly to mobile data communication methods and apparatus, especially long-range wireless data communication methods and apparatus, such as air-to-ground data communication methods and apparatus.

Background of the Invention

Modern data communications systems typically use data packets to transmit digital data, and data packets are usually transmitted in data frames called symbols. For example, a data frame in the long term evolution (LTE) standard has a standard duration of 10ms, with each data frame comprising 1 0 sub-frames each having a standard duration of 1 ms. Moreover, each sub-frame contains two slots each having a standard duration of 0.5ms.

For a multi-user data communication system, for example, a multiple-input-multiple-output (MIMO) system, a plurality of mobile users will communicate with a base station. In a modern data communication system, system resources are typically shared by a plurality of users by the system allocating different codes (or code sequence), frequencies, or times to different users. In many such systems, it is necessary for a user to request for initial uplink access to the base station in order to begin data transmission to the base station and empty or gap times are included in data frame structures to facilitate a plurality of users can be connected to the same system or BS at the same time. For example, in the Long Term Evolution (LTE) standards, uplink access is implemented by way of PRACH (physical random access channel) to facilitate request for initial uplink access, or to re-establish uplink synchronization, by a mobile terminal, also known as a 'user equipment' (UE), to a base station (BS). As shown in Figure 1 , each PRACH symbol is preceded by a cyclic prefix (CP), followed by a sequence (Seq) in subband and appended by a guard time (GT) of empty time or gap time. CP is adapted to effectively eliminate inter-symbol interference (ISI) while GT is adapted to avoid data loss and to reduce interference caused by propagation delay. In general, cyclic prefix refers to the prefixing of a symbol with a repetition of the end. The LTE facilitates multi-user connection by allocating different sequences (SEQ), time or subband to different UE. It is noted that the LTE and other currently available mobile data communication methods are not satisfactory for long range multi-user data communication systems. For example, the communication range of the LTE is only 100km. Summary of Invention

Accordingly, there is provided a data communication method between a user equipment (UE) and a base station (BS), wherein the BS is set to begin to transmit downlink data at regular time intervals T; wherein the method comprises the UE beginning to transmit uplink access data packets to access the BS at transmission times which are determined with reference to distance information between the BS and the UE to compensate for delay time for data travelling between the BS and the UE.

There is also provided mobile data communication apparatus comprising a data receiver, a data transmitter and a processor, wherein the BS is set to begin to broadcast downlink data at regular time intervals T and the UE is set to begin transmission of uplink access data packets at a time equal to T minus an adjustment time Tadj after the initial receipt time of the broadcasted downlink data of the BS, and wherein the adjustment time is set to compensate or partly compensate for propagation time delay due to data travelling between the UE and BS such that the uplink access data sent from the UE will arrive at the BS within a detection window of BS.

This method and apparatus extend the data communication range to beyond 100 km, for example, up to 200km or 300km, to facilitate the deployment of more efficient and long-range mobile data communication systems, such as air-to-ground data communications systems or data communication system for high-speed trains.

In an example, the BS is set to begin to broadcast downlink data at regular time intervals T and the UE is set to begin transmission of uplink access data packets at a time equal to T minus an adjustment time T_adj after the initial receipt time of the broadcasted downlink data of the BS, and wherein the adjustment time is set to compensate or partly compensate for propagation time delay due to data travelling between the UE and BS such that the uplink access data sent from the UE will arrive at the BS within a detection window of BS.

For example, the BS may be adapted to begin downlink data broadcast at times T_n, where T_n= T₀+nT, T₀ is the BS initial broadcast time, T is the BS broadcast time interval, and n is an integer; wherein the uplink access data of the UE comprises a cyclic prefix CP portion having a CP duration time of T_cp, and the UE is adapted to begin to transmit the uplink access data to the BS after receipt of a data packet which is sent by BS at T, such that the data packet sent by the UE will arrive at BS at a time of within T_cp of T_i+i , where i is an integer.

As a convenient example, the adjustment time T_adj may be set to equal to or greater than the return delay time 2T_d between BS and UE minus T_cp, that is, T_adj >=2T_d -Tcp, preferably T_adj >=2T_d -T_cp/2 to allow for GPS data inaccuracy or to cater for movement of the UE between the time of detection of BS data and the time to begin data transmission.

Brief Description of Drawings

Examples of data communication methods and apparatus according to the present invention and airplanes using such methods and apparatus will be described below by way of example with reference to the accompanying drawing, in which:-

Figure 1 is a schematic diagram of a data frame for typical PRACH implementation,

Figure 2 is a schematic diagram of an example air-to-ground communication system in which three airplanes are in data communication range with a base station,

Figure 3 is a schematic diagram illustrating uplink transmission time delay due to data propagation time between a UE and a BS,

Figures 4A and 4B are schematic diagram depicting correlation between propagation time delays for UE1 , UE2 and UE3 and PRACH window, Figures 5A and 5B are schematic diagrams depicting UE adjusting transmission time to mitigate propagation delay loss and an example of over-adjustment due to data inaccuracy, and Figure 6A to 6C are schematic diagrams depicting data arrival times from UE1 to UE3 with transmission begin time adjusted.

Detailed Description of embodiments

An air-to-ground radio communication system depicted in Figure 2 as an example of a multi-user data communication system comprises a first airborne plane UE1 , a second airborne plane UE2, and a third airborne plane UE3. The three airborne planes, as an example of a plurality of mobile user equipment (UE), are adapted to be in radio data communication with a base station BS which is situated on the ground. This example air-to-ground system is part of a complete air-to-ground data communication system which comprises a plurality of base stations deployed on the ground along a flight path of airplanes so that airplanes flying along a flight path can maintain radio data communication with the ground via the base stations during flight. In the example system of Figure 2, the airplanes UE1 , UE2, and UE3 are respectively at distances of 10km, 100km and 300km from the base station. The example distance have been selected to provide useful illustration because a commercial airliner usually flies at a height of 10km about the sea level when in data communication with a base station intermediate departing and destination airports, and a communication range of up to more than 100 km is desirable so that only a reasonable number of base stations need to be deployed. For example, when the communication range is 300km, only a total of 11 base stations are required to cover a path distance of 3,000km which is approximately the distance between Hong Kong and Beijing.

Similar to many mobile data communication systems, the BS of an air-to-ground data communication will make downlink broadcasts at regular time intervals T (the data frame time) by sending a data symbol to the surrounding air space at times T_n=T₀+nT, wherein T₀ is the initial broadcasting time and n is an integer so that mobile user equipment (UE) within a communication range of the BS can make data communication or data exchange with the BS. Referring to Figure 3, a data packet sent by the BS at time T₀ will reach the UE after a delay time T_d due to propagation time delay of the data packet travelling in air. This propagation delay time T_d is equal to d/c, where d is the distance of separation between UE and BS, and c is the speed of light in air. For example, the propagation delay time for a separation distance of 100km will be around 333.3 με, which is quite significant when compared to a data subframe time of 1 ms. When UE detects a data symbol from the BS, the UE will be in a position to begin data communication with BS, but will normally wait until the next scheduled transmission time to begin data transmission. For modern data communication systems including the LTE, the UE will determine the next scheduled transmission time with reference to its local time (as set by the plane's own local clock). Typically, the next scheduled transmission time is set to begin at T after the time of initial arrival of BS data at the UE. For a data transmitted at T₀ from the BS, the initial data arrival time at the UE will be at T₀+T_d due to propagation time delay, and the next scheduled transmission time of the UE to begin transmission of data to the BS is therefore set at T₀+T+T_d, or at T-i + T_d, as depicted in the lower row of Figure 3. The data packet transmitted by the UE will arrive at the BS with another propagation delay time T_d. As a result, the data sent by the UE at T-i + T_d will arrive at the BS at time T-i + 2T_d. In other words, the UE data will arrive at the BS with a delay time of 2T_d from the scheduled BS detection time of T-i . However, when the separation distance d between UE and BS is such that the return time delay (2T_d) is larger than the cyclic prefix time T_cp of CP in the data packet, BS will experience difficult in detecting this incoming data frame. Indeed, this is the underlying problem why LTE can not detect a user at 1 00km or more away from a BS.

Referring to the 3-airplane example of Figure 2, the planes UE1 , UE2, and UE3 are respectively at arbitrary distances d1 , d2 and d3 from BS, and the respective propagation delay time from BS will be T_di , T_d2, and T_d3, where T_d3 > T_d2 > Tdi since d3 > d2 >d1 . The data symbols used in this air-to-ground data communication system example are similar to those used in modern day data communication systems such as the LTE standards as shown in Figure 1 and comprise a data structure having CP, SEQ and GT where CP and GT are for the same general functions. BS is set to begin to transmit data periodically at T_n, where T_n= To+nT, T₀ is the BS initial transmission time, T is the BS transmission time interval and n is an integer. For example, when the BS begins to broadcast data packets at time Ti, the first BS data packet will arrive at the individual airplanes UE1 , UE2, and UE3 at different times of T_d__Uei , T_{d ue}2, and T_d__Ue3 respectively as shown in Figure 4A due to propagation time delay.

Using a convenient example that UE1 , UE2 and UE3 are respectively airborne at d1 =10km, d2=100km and d3=300km from the BS, the propagation time delay between UE1 and BS is negligibly small (~0) and the time of data reception will be equal to T₀. On the other hand, the delay times between BS and UE2, and between BS and UE3 would be in the milliseconds (ms) range and not negligible. For example, the return time delay (2T_d) for UE2 and UE3 would be 666.6 με and 2ms respectively.

As shown in a PRACH detection window depicted in Figure 4B, when the return time delay 2T_{d ue2} is equal to the time duration T_cp of CP, the uplink data from UE2 is still marginally receive-able by BS, as the truncated data portion is remediable by the CP portion of the data. On the other hand, when the return time delay 2T_{d ue3} exceeds the time duration T_cp of CP, the uplink data from UE3 is not receive-able by BS, since the truncated data portion is no longer remediable by the CP portion of the data.

To mitigate the risks of data loss due to propagation time delay, an airplane as an example of a mobile UE is set to begin to transmit data to the BS with time adjustments to compensate for the propagation delay such that the data sent by the UE upon receipt of data broadcast from the BS are detectable by the BS. As the data loss is linked to the return path propagation delay time 2T_d, which is due to separation distance d between the BS and a UE, a UE is set to adjust the data transmission time by taking into consideration the propagation delay time such that a data packet sent by the UE upon receipt of a data broadcast by the BS will arrive at the BS and detectable by BS. In general, BS is scheduled to begin to make data broadcast and to detect incoming data at regular times T_n=T₀+nT. As a detection or reception window (W) of T_Cp is provided to allow for detection of data carrying a propagation delay, a data sent by the UE will be detectable as long as the arrival time at BS is within a time window of T_cp from a scheduled time T_n. Therefore, by adjusting the UE transmission time such that a data will arrive at BS at a time inside the reception window W of Figure 5 data loss will be mitigated. For the example of Figure 5A, the width of the detection W from T_i+i is T_cp in response to a data sent from the BS in the time frame beginning at T,.

In an implementation example, UE is set to transmit at T minus an offset time or adjustment time T_adj (i.e., T- T_adj) after the initial arrival time at UE at T_n+T_d of a data sent from BS at T_n to compensate or partly compensate for the return delay time, and the offset time T_adj would be 2T_d or less, such that a data sent in the time frame beginning at T_n will arrive at the BS within the reception window of T_cp of T_n. In mathematical forms, the time adjustment relationship will be 0<=2T_d - T_adj <= T_cp, or

By bringing forward the transmission begin time of the UE at a time of T_adj before the originally scheduled transmission begin time, data from UE1 , UE2, and UE3 and having the propagation delay relationships as shown in Figures 6A and 6B will all arrive at the BS with the detection reception time window W as shown in Figure 6C.

In a further implementation example, the separation distance between the BS and UE is obtained by ascertaining the spatial location information of the BS and UE, for example, by deducing the separation distance between BS and UE from the spatial coordinates. As an implementation example, the BS is adapted to broadcast its location information for reception by an airplane within the communication range and the airplane can use the spatial location information to deduce the separation distance between UE and BS. For example, the BS can broadcast its global positioning satellite (GPS) information to the airplanes in a downlink synchronization channel to facilitate processing. In another implementation example, the spatial location information of the BS can be stored on the airplane and can be retrieved once the identity of the BS is known, for example, by the BS broadcasting its identity (ID), since only a small number of BS is distributed alone the flight path in the case of air-to-ground communication systems.

As an example, the distance (d) for calculating the uplink access data transmission adjustment time can be obtained from the GPS information as follows:

In another example, the distance covered by an airplane between the time of initial detection of the downlink data from the BS and the beginning of transmission of uplink access data is also taken into consideration. For example, for an airplane moving at 1000km/h, the distance covered in a typical transmission cycle of 1 second would be around 278m. The movement distance can be taken into account with reference to the moving direction of the airplane to fine tune the distance d when calculating the transmission begin adjustment time without loss of generality.

While the GPS provides high precision information, it is known that inaccuracies are still present in such information. For example, there will be inaccuracies in GPS coordinates which are known to be accurate to within a deviation distance of 100m, and there will be inaccuracies due to GPS downlink data refreshing times which could cause a deviation distance of up to 500m. In general, such inaccuracies would not be critical or even important when the CP and GT can support a distance of 20km. In situations where the time adjustments are made such that the uplink access data from the UE is calculated to arrive exactly at time T_i+ , that is aligned with the data transmission time of the BS, but an error time T_e is present, the uplink access data will arrive at a time 2T_e before time T_i+ as shown in Figure 5B, thereby rendering the data undetectable by the BS. To alleviate the situation of Figure 5B due to over-adjustment of transmission begin time when such inaccuracies may be present, the adjustment time may be set with a margin as follows:

With such a safety margin for the adjustment time, the data will arrive within the detection window of T_i+ as shown in Figure 5C.

While the present invention has been described with reference to the above examples, it would be appreciated by persons skilled in the art that the examples are only provided as illustrations to assist understanding and are not meant to restrict scope of invention. For example, while three airplanes at different distances from a BS have been described as an example of a plurality of mobile UE, it would be appreciated that other number of airplanes could make data communication with a single BS without loss of generality. For example, up to 10 airplanes can be in communication with a single BS at the same time. Furthermore, while airplanes have been used as an example of an air-to-ground or ground-to-air data communication system, the principles described herein are equally applicable to other long range multi-user data communication systems such as those for high speed trains travelling at 200-300km/h. Furthermore, while a ground station has been used as an example of a BS, it would be appreciated that the BS can also be mobile without loss of generality.

Claims

A data communication method between a user equipment (UE) and a base station (BS), wherein the BS is set to begin to transmit downlink data at regular time intervals T; wherein the method comprises the UE beginning to transmit uplink access data packets to access the BS at transmission times which are determined with reference to distance information between the BS and the UE to compensate for delay time for data travelling between the BS and the UE.

A data communication method according to Claim 1 , wherein the method comprises the UE determining distance between BS and UE with reference to the distance information between the BS and the UE.

A data communication method according to Claim 2, wherein the distance information contains spatial location information of the BS and UE.

A data communication method according to Claim 3, wherein the spatial location information of the BS and the UE contains the spatial coordinates of BS and UE.

A data communication method according to Claim 4, wherein the spatial coordinates of the BS and UE are obtained by precision positioning systems such as the global positioning satellites (GPS).

A data communication method according to any of the preceding Claims, wherein the method comprises the BS transmitting its spatial coordinates via an downlink broadcast or data channel.

A data communication method according to any of the preceding Claims, wherein the method comprises the UE getting its instantaneous spatial coordinates from the GPS to calculate its instantaneous distance from the BS.

8. A data communication method according to any of the preceding Claims, wherein the method comprises the BS sending its spatial location information to the UE, and the UE processing the received BS spatial location information with reference to its instantaneous location information to obtain the distance information and to determine the time to begin transmission of the uplink access data packets.

9. A data communication method according to any of the preceding Claims, wherein the BS is set to begin to broadcast downlink data at regular time intervals T and the UE is set to begin transmission of uplink access data packets at a time equal to T minus an adjustment time T_adj after the initial receipt time of the broadcasted downlink data of the BS, and wherein the adjustment time is set to compensate or partly compensate for propagation time delay due to data travelling between the UE and BS such that the uplink access data sent from the UE will arrive at the BS within a detection window of BS.

10. A data communication method according to Claim 9, wherein the adjustment time Tadj is equal to or less than the return delay time 2T_d for data to travel in air between BS and UE.

1 1 . A data communication method according to any of the preceding Claims, wherein BS is adapted to begin downlink data broadcast at times T_n, where T_n= To+nT, To is the BS initial broadcast time, T is the BS broadcast time interval, and n is an integer; wherein the uplink access data of the UE comprises a cyclic prefix CP portion having a CP duration time of T_cp, and the UE is adapted to begin to transmit the uplink access data to the BS after receipt of a data packet which is sent by BS at T, such that the data packet sent by the UE will arrive at BS at a time of within T_cp of T_i+ , where i is an integer. 12. A data communication method according to Claim 11 , wherein the adjustment time Tadj is equal to or greater than the return delay time 2T_d between BS and UE minus T_cp, that is, T_adj >=2T_d -T_cp.

13. A data communication method according to any of the preceding Claims, wherein the movement distance of the UE during the time between the time of initial receipt of downlink data from the BS to the time of transmission of uplink access data to the BS is also accounted for in the distance information.

14. A data communication method according to any of the preceding Claims, wherein the UE is an air-borne airplane or a high-speed moving train.

15. A data communication method according to any of the preceding Claims, wherein the data communication range between the UE and the BS exceeds

100km.

1 6. A mobile data communication apparatus comprising a data receiver, a data transmitter and a processor, wherein the apparatus (UE) is adapted to communicate with a base station BS which is set to begin to transmit downlink data at regular time intervals T; wherein the apparatus is adapted such that the transmitter begins to transmit uplink access data packets to access the BS at transmission times which are determined with reference to distance information between the BS and the UE to compensate for delay time for data travelling between the BS and the UE.

17. A mobile data communication apparatus comprising a data receiver, a data transmitter and a processor, wherein the the BS is set to begin to broadcast downlink data at regular time intervals T and the UE is set to begin transmission of uplink access data packets at a time equal to T minus an adjustment time T_adj after the initial receipt time of the broadcasted downlink data of the BS, and wherein the adjustment time is set to compensate or partly compensate for propagation time delay due to data travelling between the UE and BS such that the uplink access data sent from the UE will arrive at the BS within a detection window of BS.

18. A mobile data communication apparatus according to Claim 17, wherein the adjustment time T_adj is equal to or less than the return delay time 2T_d for data to travel in air between BS and UE.

19. A mobile data communication apparatus according to any of the preceding Claims 16-18, wherein BS is adapted to begin downlink data broadcast at times T_n, where T_n= T₀+nT, T₀ is the BS initial broadcast time, T is the BS broadcast time interval, and n is an integer; wherein the uplink access data of the UE comprises a cyclic prefix CP portion having a CP duration time of T_cp, and the UE is adapted to begin to transmit the uplink access data to the BS after receipt of a data packet which is sent by BS at T, such that the data packet sent by the UE will arrive at BS at a time of within T_cp of T_i+i , where i is an integer.

20. A mobile data communication apparatus according to Claim 19, wherein the adjustment time T_adj is equal to or greater than the return delay time 2T_d between BS and UE minus T_cp, that is, T_adj >=2T_d -T_cp. An aircraft comprising a mobile data communication apparatus according to any of Claim 1 6-20 adapted to perform data communication with a BS according to any of the methods according to Claims 1 - 15.