WO2017036529A1

WO2017036529A1 - Techniques to reduce guard period overhead in wireless networks

Info

Publication number: WO2017036529A1
Application number: PCT/EP2015/070126
Authority: WO
Inventors: Gilberto BERARDINELLI; Frank Frederiksen; Klaus Ingemann Pedersen; Preben Elgaard Mogensen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-09-03
Filing date: 2015-09-03
Publication date: 2017-03-09

Abstract

A technique may include receiving, by a base station, signals from a user device, determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device, and transmitting, by the base station to the user device, downlink signals during the user device- specific downlink transmission period.

Description

Techniques To Reduce Guard Period Overhead In Wireless Networks

TECHNICAL FIELD

[0001] This description relates to communications.

BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3^rd Generation Partnership Project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. E- UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations or access points

(APs), which are referred to as enhanced Node AP (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments.

[0004] A global bandwidth shortage facing wireless carriers has motivated the consideration of the underutilized millimeter wave (mmWave) frequency spectrum for future broadband cellular communication networks, for example. mmWave (or extremely high frequency) may, for example, include the frequency range between 30 and 300 gigahertz (GHz). Radio waves in this band may, for example, have wavelengths from ten to one millimeters, giving it the name millimeter band or millimeter wave. The amount of wireless data will likely significantly increase in the coming years. Various techniques have been used in attempt to address this challenge including obtaining more spectrum, having smaller cell sizes, and using improved technologies enabling more bits/s/Hz, and/or allowing a more efficient use of resources. One element that may be used to obtain more spectrum is to move to higher frequencies, above 6 GHz. For fifth generation wireless systems (5G), an access architecture for deployment of cellular radio equipment employing mm Wave radio spectrum has been proposed. Other example spectrums may also be used, such as cmWave radio spectrum (3-30 GHz).

SUMMARY

[0005] According to an example implementation, a method may include receiving, by a base station, signals from a user device; determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0006] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a base station, signals from a user device; determine, by the base station, a length of a user device- specific downlink transmission period for transmitting from the base station to the user device; transmit, by the base station to the user device, downlink signals during the user device- specific downlink transmission period.

[0007] According to another example implementation, a computer program product may include a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including receiving, by a base station, signals from a user device; determining, by the base station, a length of a user device- specific downlink transmission period for transmitting from the base station to the user device; and, transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0008] According to another example implementation, an apparatus may include means for receiving, by a base station, signals from a user device; means for determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and, means for transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0009] According to an example implementation, a method may include: receiving, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device; and receiving, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0010] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device; and receive, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0011 ] According to another example implementation, a computer program product may include a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including receiving, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device; and receiving, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0012] According to another example implementation, an apparatus may include means for receiving, by a user device from a base station, an indication of a user device- specific downlink transmission period for the user device; and means for receiving, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0013] The details of one or more examples of implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG 1 is a block diagram of a wireless network according to an example implementation.

[0015] FIG. 2 is a diagram illustrating a network in which multiple user devices/UEs are located at different distances from the base station (BS).

[0016] FIG. 3 is an example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which one guard period (GP) is used for all user devices/UEs of the cell or network.

[0017] FIG. 4 is a flow chart illustrating operation of a base station according to an example implementation.

[0018] FIG. 5 is a flow chart illustrating operation of a user device/user equipment (UE) according to an example implementation.

[0019] FIG. 6 is an example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which a UE-specific downlink transmission period and an associated UE-specific guard period (GP) may be determined for each UE of the cell or network according to an example implementation.

[0020] FIG. 7 is another example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which a UE-specific downlink transmission period and an associated UE-specific guard period (GP) may be determined for each UE of the cell or network according to an example implementation.

[0021 ] FIG.8 is a block diagram of a wireless station (e.g., base station access point or mobile station/user device/user equipment) according to an example implementation.

DETAILED DESCRIPTION

[0022] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation. In the wireless network 130 of FIG. 1, user devices 131, 132, 133 and 135, which may also be referred to as mobile stations (MSs) or user equipment (UEs), may be connected (and in communication) with a base station (BS) 134, which may also be referred to as an Access Point (AP) or an enhanced Node B (eNB). At least part of the functionalities of a base station (BS), access point (AP) or (e)Node B (eNB) may be also be carried out by any node, server or host which may be operably coupled to a transceiver, such as a remote radio head. BS 134 provides wireless coverage within a cell 136, including to user devices 131 , 132, 133 and 135. Although only four user devices are shown as being connected or attached to BS 134, any number of user devices may be provided. BS 134 is also connected to a core network 150 via a SI interface 151. This is merely one simple example of a wireless network, and others may be used.

[0023] A user device (or user terminal, or user equipment (UE)) may refer to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (MS), a mobile phone, a cell phone, a smartphone, a personal digital assistant (PDA), a handset, a device using a wireless modem (alarm or measurement device, etc.), a laptop and/or touch screen computer, a tablet, a phablet, a game console, a notebook, and a multimedia device, as examples. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be referred to herein as a user equipment (UE).

[0024] In LTE (as an example), core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility /handover of user devices between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the Internet, and other control functions or blocks.

[0025] The various example implementations may be applied to a wide variety of wireless technologies or wireless networks, such as LTE, LTE-A, 5G, cmWave, and/or mmWave band networks, or any other wireless network. LTE, 5G, cmWave and mm Wave band networks are provided only as illustrative examples, and the various example implementations may be applied to any wireless technology/wireless network.

[0026] In a wireless network, such as, for example, a time division duplex (TDD) radio system, a guard period (GP) is typically used for providing a time gap or time separation between a downlink (DL) transmission and an uplink (UL) transmission for a user device/UE. In some cases, the GP may provide a time period to allow for one or more of the following, for example:

[0027] 1) Accommodating the turnaround time, e.g., the on/off (and off/on) power transient of the receiver (transmitter) circuitry of the user device/UE;

2) Compensating for the propagation delay of the DL signal from the BS to the user device/UE; and/or,

3) Allowing the user device(s)/UEs to begin their transmission earlier than the UL scheduled slot/UL subframe (e.g., based on the timing advance offset assigned to each user device/UE).

[0028] In wireless/radio technologies, such as Long Term Evolution (LTE), as an illustrative example, the start time for uplink (UL) transmission for each user device/LTE is adjusted by a Timing Advance (TA) command (which identifies a timing advance offset) according to the user device's distance from the BS (or according to a UE-BS propagation delay). The aim is, for example, to align at the BS the signals received from the multiple UEs despite the different propagation delays for each UE, since each UE in a cell/network may be located a different distance from the BS. The timing advance offset may indicate a time period in front of or before the UL scheduled slot (e.g., UL subframe or scheduled UL transmission period) that the UE should begin its UL transmission, so that all received UL data at the BS will be aligned (or received at the BS at approximately the same time, e.g., to avoid interference at the BS).

[0029] Since the propagation delay for a certain user device/UE is the same for both UL and DL, the required GP duration may be described, for example (other GP definitions may also be used), as:

[0030] T_GP > δ + where S denotes the turnaround time, d is the physical distance between the user device/UE and the BS antenna, and c is the speed of light.

[0031 ] In the illustrative example case of a large cell (e.g., with coverage range of up to -100 km, for example) operating in TDD (time division duplex) mode, user devices/UEs can be located at very different distances from the BS. In order to serve all the user devices/UEs, if one common GP is used for all user devices/UEs in the cell/network, the GP may typically be set according to the worst case scenario - that is, according to the

UE(s) with the largest distance from the BS (or otherwise determined based on the distance from the BS to the cell edge). For example, in the case of a UE located at a 100 km distance from the BS, the required GP duration is of around 0.7 ms (assuming a 20 μ8 turnaround time). However, such a long GP may penalize the user devices/UEs that are closer to the BS. For example, in the case of a user device/UE located at 50 m from the BS, a GP duration of around 21 would be sufficient, and using a GP significantly longer than this duration (around 21 s) for this nearby /close user device/UE may result in significant idle period and/or waste of some resources for this nearby user device/UE, for example.

[0032] FIG. 2 is a diagram illustrating a network in which multiple user devices/UEs are located at different distances from the base station (BS). A BS 134 provides wireless coverage within a cell. Multiple user devices/UEs are connected and receiving wireless services from BS 134, including, for example: UEA at a distance dA from BS 134, UE_B at a distance d_B from BS 134, and UE_C at a distance d_c from BS 134. In this illustrative example, UE_A is the closest to BS 134, and UE_C is the farthest from the BS 134, such that d_A « d_B « d_c . UE< may be, for example, located at the cell edge. I one common GP is used for all user devices/UEs within this cell, the BS 134 may set a GP duration for the cell equal to T_GP≥ δ + since this provides a GP that provides sufficient buffer time/guard period for all user devices/UEs within the cell. Thus, for example, in some cases, a GP may be set based on the distance or range to the cell edge and/or to the farthest user device/UE. While using the worst case (or farthest user device/UE) as a basis to determine the GP for the cell provides sufficient GP for all user devices/UEs, it has the disadvantage of causing significant idle period for user devices/UEs that may be relatively close to the BS (e.g., resulting in some wasted/unused resources for such UEs), since such a long GP is typically unnecessary for user devices/UEs that are near the BS 134. Each UE may have a different UE-BS propagation delay. For example, UE_A, which is the closest to the BS, has a relatively short UE-BS propagation delay, while UEc, which is the farthest from the BS, has a relatively long UE-BS propagation delay. In some example implementations, the GP may be set as a common value for the entire network (such that the uplink timing is common for all UE in the network). In such a case, the GP may be defined, for example, according to the worst condition in the entire network or cell (e.g., distance or propagation delay to cell edge), rather than the worst condition UE (e.g., farthest UE) in the cell.

[0033] FIG. 3 is an example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which one guard period (GP) is used for all user devices/UEs of the cell or network. As shown in FIG. 3, the upper three rows indicate data or signals from the BS perspective 310, while the lower three rows indicate data or signals from the UE perspective 320. As shown in FIG. 3, BS 134 transmits downlink signals to each of the three UEs during a DL portion or a DL transmission period 332, where, e.g., a different frequency or set of frequencies may be used to transmit to each UE. For example, UE_A, which is the closest to the BS, has a relatively short UE-BS propagation delay 340A, while UEc, which is the farthest from the BS, has a relatively long UE-BS propagation delay 340C. From the BS perspective 10, a guard period (GP) 334 is provided between DL and UL transmissions, e.g., a GP 334 may be provided between an end of DL transmission and a beginning of LTL reception by the BS. Thus, GPs 334A, 334B and 334C provided for UE_A, UE_B and UE_C, respectively, are the same length GP. That is, in this example, one common GP 334 (having the same length GP for all UEs in the cell or network) may be established or used, e.g., based on the farthest UE or the cell edge, for example.

[0034] As shown in FIG. 3, the three UEs are transmitting (Tx) and receiving (Rx) their data and control information over a portion of the available frequency band. Given their different distances from the BS (and thus, different propagation delays), the UEs (UEA, UE_b and UE_C) will begin (and end) receiving useful information at different time instants, invading part of the GP 334. Thus, for example, the DL transmission period 332 is the same for each UE, and each DL transmission signal is of the same length as received by each UE, e.g., DL transmission periods (viewed as a DL receiving periods by UE) 350A, 350B, 350C for LTE_A, UE_B and UE_C, respectively, are the same length. This is because the GP (334A, 334B and 334C) for each FTE is the same length in this example.

[0035] As shown in FIG. 3, the UEs will also start their respective UL

transmissions at different time instants, depending on their specific TA (timing advance or timing advance offset) settings, such that their signals can be receive-aligned at the BS (DL signals from the UEs received at approximately the same time. Because UEA is located at a short distance, it will start its transmission only with a slight advance (short timing advance offset) 344A with respect to the allocated UL slot, while UE_B and UEc need to start their transmission earlier). For example, UE_C may begin its UL transmission at a timing advance offset 344C, which is larger than timing advance offset 344A. As shown in FIG. 3, only UE_cis exploiting the entire GP (the blank gap 342 between the arrows is only meant to cope with the turnaround time for UE_C), while the GP duration is certainly excessive for the other UEs. Correspondingly, UE_A is experiencing a somewhat long "idle" period 346A during the GP, as it needs only a small timing advance to compensate for its relatively short UE-BS propagation delay.

[0036] Therefore, as can be seen in the diagram of FIG. 3, providing one GP for a cell or network, e.g., setting the GP according to the cell radius or based on a UE that is farthest from the BS, may introduce an unnecessary overhead for other UEs in the cell, which are then penalized in terms of resource utilization.

[0037] Therefore, according to an example implementation, a per-UE guard period (GP) may be determined by the BS 134, such that a more efficient use of resources may be obtained. For example, a user device/UE- specific GP may be determined by the BS for each UE in a cell or network based on various measurements, e.g., based on: 1) a distance the user device/UE is from the BS, 2) a UE-BS propagation delay for each UE, 3) received signal strength or received signal power (which may be used to estimate distance that a UE is from a BS or to estimate UE-BS propagation delay), e.g., based on a received signal power/received signal strength for signals received by the BS from each UE or based on strength/power of signals received by each UE and reported to the BS, or other measurement technique, for example. For example, the BS 134 may determine a UE-BS propagation delay based on reference signals received from each UE, based on a random access sequence/request sent by each UE to the BS, or based on other signals transmitted by each UE to the BS 134. According to an example implementation, by selecting or determining a different or variable (UE-specific) GP for each UE, the BS 134 also determines an associated UE-specific DL transmission period for each UE. Thus, for UEs that are far away from the BS, e.g., having a longer UE-BS propagation delay, a relatively long GP is used and an associated relatively short DL transmission period, whereas for UEs that are relatively close to or nearby the BS, a much shorter GP and an associated longer DL transmission period may be used to allow a greater use of resources and avoid the undesirable large idle period 346A shown in FIG. 3, for example.

[0038] FIG. 4 is a flow chart illustrating operation of a base station according to an example implementation. Operation 410 may include receiving, by a base station, signals from a user device. Operation 420 may include determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device. And, operation 430 may include transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0039] According to an example implementation of the method of FIG. 4, the determining, by the base station, a length of a user device-specific downlink transmission period for the user device also determines a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

[0040] According to an example implementation of the method of FIG. 4, wherein, for the user device, the length of the user device-specific downlink transmission period plus the length of the associated guard period is a fixed period of time, such that a greater length of the user device-specific downlink transmission period provides a shorter associated guard period, and wherein a shorter length of the user device- specific downlink transmission period provides a longer associated guard period for the user device.

[0041 ] According to an example implementation of the method of FIG. 4, the determining may include: determining, by the base station, an ending point of a user device-specific downlink transmission period for the user device, wherein a starting point for the user device-specific downlink transmission period for the user device is fixed.

[0042] According to an example implementation of the method of FIG. 4, the determining may include: determining, by the base station, a propagation delay between the user device and the base station based on the signals received from the user device; and determining the length of the user device- specific downlink transmission period for the user device based on the propagation delay.

[0043] According to an example implementation of the method of FIG. 4, wherein a shorter propagation delay between the user device and the base station provides for a longer user device-specific downlink transmission period and a shorter associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device; and wherein a longer propagation delay between the user device and the base station provides for a shorter user device- specific downlink transmission period and a longer associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device.

[0044] According to an example implementation of the method of FIG. 4, wherein the determining may include: determining, by the base station based on the received signals, a timing advance offset for the user device; and, determining a user device- specific downlink transmission period for the user device based on the timing advance offset for the user device.

[0045] According to an example implementation of the method of FIG. 4, the method may further include sending, from the base station to the user device, a message indicating the user device-specific downlink transmission period for the user device. Also, the user device- specific downlink transmission period (transmission from the BS, from the BS perspective) corresponds to (is the same period as) a user device-specific downlink reception period (a reception period, from the UE perspective). Thus, this user device- specific period may be referred to as either a user device-specific downlink transmission period (e.g., from the BS perspective, since the BS is transmitting during this period) or a user device-specific downlink reception period (e.g., from the UE perspective, since the UE/user device is receiving during this period).

[0046] According to an example implementation of the method of FIG. 4, the method may include: receiving, by a base station, signals from a first user device and from a second user device; determining, by the base station, a first propagation delay between the first user device and the base station; determining, by the base station, a second propagation delay between the second user device and the base station; determining, by the base station based on the first propagation delay, a length of a first user device-specific downlink transmission period for transmitting from the base station to the first user device; determining, by the base station based on the second propagation delay, a length of a second user device-specific downlink transmission period for transmitting from the base station to the second user device; providing, by the base station to the first user device, an indication of the length of the first user device- specific downlink transmission period; and providing, by the base station to the second user device, an indication of the length of the second user device-specific downlink transmission period.

[0047] According to an example implementation of the method of FIG. 4, the determining may include: determining, by the base station, a length of a user device- specific downlink transmission period for the user device based on at least one of the following: a propagation delay between the user device and the base station; a location of the user device relative to the base station; a distance between the user device and the base station; and a received signal strength or received power for a signal receive by the base station from the user device.

[0048] An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by a base station, signals from a user device; determine, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and, transmit, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0049] According to another example implementation, a computer program product may include a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including receiving, by a base station, signals from a user device; determining, by the base station, a length of a user device- specific downlink transmission period for transmitting from the base station to the user device; and, transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0050] According to another example implementation, an apparatus may include means (e.g., 802A/802B and/or 804, FIG. 8) for receiving, by a base station, signals from a user device; means(e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and, means (e.g., 802A/802B and/or 804, FIG. 8) for transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

[0051 ] According to an example implementation of the apparatus, the means for determining, by the base station, a length of a user device-specific downlink transmission period for the user device comprises means (e.g., 802A/802B and/or 804, FIG. 8) for determining a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

[0052] According to an example implementation of the apparatus, the length of the user device-specific downlink transmission period plus the length of the associated guard period is a fixed period of time, such that a greater length of the user device-specific downlink transmission period provides a shorter associated guard period, and wherein a shorter length of the user device-specific downlink transmission period provides a longer associated guard period for the user device.

[0053] According to an example implementation of the apparatus, the means for determining may include means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, an ending point of a user device-specific downlink transmission period for the user device, wherein a starting point for the user device- specific downlink transmission period for the user device is fixed.

[0054] According to an example implementation of the apparatus, the means for determining may include means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, a propagation delay between the user device and the base station based on the signals received from the user device; and means (e.g., 802A/802B and/or 804, FIG. 8) for determining the length of the user device-specific downlink transmission period for the user device based on the propagation delay.

[0055] According to an example implementation of the apparatus, wherein a shorter propagation delay between the user device and the base station provides for a longer user device-specific downlink transmission period and a shorter associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device; and wherein a longer propagation delay between the user device and the base station provides for a shorter user device-specific downlink transmission period and a longer associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device.

[0056] According to an example implementation of the apparatus, the means for determining may include: means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station based on the received signals, a timing advance offset for the user device; and, means (e.g., 802A/802B and/or 804, FIG. 8) for determining a user device-specific downlink transmission period for the user device based on the timing advance offset for the user device.

[0057] According to an example implementation of the apparatus, the apparatus may further include means (e.g., 802A/802B and/or 804, FIG. 8) for sending, from the base station to the user device, a message indicating the user device-specific downlink transmission period for the user device.

[0058] According to an example implementation of the apparatus, the apparatus may include means (e.g., 802A/802B and/or 804, FIG. 8) for receiving, by a base station, signals from a first user device and from a second user device; means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, a first propagation delay between the first user device and the base station; means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, a second propagation delay between the second user device and the base station; means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station based on the first propagation delay, a length of a first user device- specific downlink transmission period for transmitting from the base station to the first user device; means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station based on the second propagation delay, a length of a second user device-specific downlink transmission period for transmitting from the base station to the second user device; means (e.g., 802A/802B and/or 804, FIG. 8) for providing, by the base station to the first user device, an indication of the length of the first user device-specific downlink transmission period; and means (e.g., 802A/802B and/or 804, FIG. 8) for providing, by the base station to the second user device, an indication of the length of the second user device- specific downlink transmission period.

[0059] According to an example implementation of the apparatus, the means for determining may include: means (e.g., 802A/802B and/or 804, FIG. 8) for determining, by the base station, a length of a user device- specific downlink transmission period for the user device based on at least one of the following: a propagation delay between the user device and the base station; a location of the user device relative to the base station; a distance between the user device and the base station; and a received signal strength or received power for a signal receive by the base station from the user device.

[0060] FIG. 5 is a flow chart illustrating operation of a user device/user equipment (UE) according to an example implementation. Operation 510 includes receiving, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device. And, operation 520 includes receiving, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0061 ] According to an example implementation of the method of FIG. 5, the receiving, by the user device from the base station, an indication of a user device-specific downlink transmission period may include: receiving, by the user device from the base station, an ending point of a user device- specific downlink transmission period for the user device.

[0062] According to an example implementation of the method of FIG. 5, the sending may include: sending, from the user device to the base station, a random access request.

[0063] According to an example implementation of the method of FIG. 5, the length of the user device-specific downlink transmission period for the user device also determines a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

[0064] According to an example implementation of the method of FIG. 5, the method may further include sending signals from the user device to the base station. The sending may be performed either before or after the operations 510 and 520, for example. The signals sent from the user device to the base station may be used, for example, to allow the BS to determine a (or an updated) timing advance offset for the user device and/or a user device-specific downlink transmission period for the user device and/or a user device- specific GP for the user device.

[0065] According to an example implementation of the method of FIG. 5, the sending may include at least one of the following: sending, from the user device to the base station, a random access request; sending, from the user device to the base station, uplink reference signals; and sending, from the user device to the base station, uplink data.

[0066] According to an example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: receive, by the user device from the base station, an indication of a user device-specific downlink transmission period for the user device; and receive, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0067] According to another example implementation, a computer program product may include a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including receiving, by the user device from the base station, an indication of a user device-specific downlink transmission period for the user device; and receiving, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.

[0068] According to another example implementation, an apparatus may include means (e.g., 802A/802B and/or 804, FIG. 8) for receiving, by the user device from the base station, an indication of a user device-specific downlink transmission period for the user device; and means (e.g., 802A/802B and/or 804, FIG. 8) for receiving, by the user device from the base station, signals during the user device- specific downlink transmission period for the user device.

[0069] According to an example implementation of the apparatus, the means for receiving, by the user device from the base station, an indication of a user device-specific downlink transmission period may include: means (e.g., 802A/802B and/or 804, FIG. 8) for receiving, by the user device from the base station, an ending point of a user device- specific downlink transmission period for the user device.

[0070] According to an example implementation of the apparatus, the means for sending may include: means (e.g., 802A/802B and/or 804, FIG. 8) for sending, from the user device to the base station, a random access request.

[0071] According to an example implementation of the apparatus, the length of the user device-specific downlink transmission period for the user device also determines a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

[0072] According to an example implementation of the method of FIG. 5, the method may further include sending signals from the user device to the base station.

[0073] According to an example implementation of the apparatus, the means for sending may include at least one of the following: means (e.g., 802A/802B and/or 804, FIG. 8) for sending, from the user device to the base station, a random access request; sending, from the user device to the base station, uplink reference signals; and means (e.g., 802A/802B and/or 804, FIG. 8) for sending, from the user device to the base station, uplink data.

[0074] According to an example implementation, the various techniques or implementations may allow for a per-UE configuration of the guard period (GP), such that it is possible for the BS to utilize and optimize each link to use a GP that matches or may be based upon the channel conditions and/or UE-specific distance from the BS and/or the UE-BS propagation delay. Thus, user devices may be scheduled to use more resources or less resources, e.g., in the time domain and/or frequency domain according to their distance from the BS. For example, in some cases a UE resource allocation/usage (e.g., length of the DL transmission period) may have an inverse relationship with their distance or propagation delay, e.g., resource allocation for a UE may increase as distance and UE-BS propagation delay increased, and UE-specific GP may have a positive correlation with distance or UE-BS propagation delay, that is, GP may be larger/greater for UEs that have a greater distance from BS or a greater propagation delay. In this manner, greater resources, e.g., a longer DL transmission period may be used or provided for UEs that are closer to the BS, resulting in a shorter associated GP, while a shorter DL transmission period may be used or provided for UEs that are farther from (having a greater propagation delay) the BS, resulting in a longer associated GP.

[0075] For example, T_DL may indicate the duration or length of a DL time slot, such as the a DL transmission that the BS spans, for instance, the time-interval [i_Qr t₀ + T_DL]. A UE located at a distance d from the BS should then only be scheduled for DL transmission within the time interval t_Q, t₀ + T_DL + T_GP— ϋ , (as a UE-specific DL transmission period).

[0076] In an example implementation, there may be no restrictions for the frequency domain DL scheduling; and there may be no restrictions for the time/frequency domain UL scheduling. This approach allows reducing the required T_cp (time or length of the GP) on a per-UE basis. According to one illustrative example, with respect to the UE positions shown in FIG. 2, the BS may determine or set a GP length/duration according to the closest UE, i.e., UE_A, T_cp ^:¾^: δ -f— . Then, the following conditions for the time domain scheduling may apply:

1) UE_A has no scheduling restrictions within the DL slot, as can be also easily derived from the expression above.

2) UE_B should be scheduled in a portion of the DL slot comprised in the interval I i_0., t₀ + T_D , + T_GP— δ - And,

3) UEc should be scheduled in a portion of the DL slot comprised in the interval

[0077] FIG. 6 is an example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which a UE-specific downlink transmission period and an associated UE-specific guard period (GP) may be determined for each UE of the cell or network according to an example implementation. In this illustrative example, because d_s « d_c, the interval (e.g., DL transmission period) for the possible allocation of

UE_B is larger than the interval (or DL transmission period) for the possible allocation of UE_C. As a consequence, UE_C may, for example, be scheduled at the first part of the DL slot, while UE_B can be scheduled for a larger part of the DL slot, but not on its last portion. Thus, for example, as shown in FIG. 6, from the BS perspective, the BS 134 transmits for a UE-specific downlink (DL) transmission period, including: BS may transmit for DL transmission period 6 IOC to UE_C, which corresponds to period 612C indicating a period that signals are received by the UEc; BS may transmit for DL transmission period 610B to UE_B, which corresponds to period 612B indicating a period that signals are received by the UE_B; and, BS may transmit for DL transmission period 610A to UE_A, which corresponds to period 612A indicating a period that signals are received by the UE_A. Thus, it can be seen from the example shown in FIG. 6 that a longer DL transmission period (of time) 610A/612A and an associated shorter GP is provided for UE_A, to allow greater use of resources for a UE that is closer to the BS (since only a short GP is required for this close UE), while a shorter DL transmission period (of time) 610C/612C and an associated longer GP is provided for UEc, for example. In an example implementation, for all of the UEs, the total time that includes the DL transmission period plus the associated GP may be a fixed time period. Thus, providing a shorter GP (e.g., associated with a shorter UE-BS propagation delay, such as for UE_A) may allow a longer/greater DL transmission period, while providing a longer GP (e.g., associated with a longer UE-BS propagation delay, such as for UEc) may allow only a shorter DL transmission period for such UE.

[0078] In the illustrative example shown in FIG. 6, given the lack of scheduling restriction, UE_A is allocated over the entire DL slot (610A), LTE_B is allocated in a rather large part (610B) of the DL slot but not in its last portion, and UEc is allocated in the initial part (6 IOC) of the DL slot 602. The resources are frequency domain multiplexed for the time portions where multiple UEs are allocated. Also, as shown in FIG. 6, frequency resources may be reallocated over time among UEs within the cell/network based on different DL transmission periods for each UE. For example, frequency resources assigned to a first UE having a short DL transmission period may be reallocated or reused for transmission to a second UE that has a greater DL transmission period. For example, this resource reallocation may occur at the end of the DL transmission period of the first UE, e.g., when the first UE no longer is using such resources. For example, as shown in FIG. 6, a first set of frequency resources (shown at 6 IOC) may be initially allocated and used to transmit to UE_C during the time period tl . At the end of time period tl (which may be at the end of the DL transmission period for UEc), the first set of frequency resources may then be reallocated to UE_B within time period t2, as shown by 610B. And, the first set of frequency resources may then be reallocated to UE_A (having the greatest DL transmission period as compared to the other UEs) within time period t3, as shown by 610 A. [0079] According to an example implementation, a GP duration may be set according to UE_A and is therefore rather short due to its short distance from the BS. UE_A is therefore the only user that exploits DL scheduling and resource utilization up to the GP. UE_B may begin receiving its allocated data with a certain delay with respect to UE_A due to the larger propagation delay. When it has received data according to the portion of the DL time slot allocated to it, it can turn off its receiver chain. In order to allow its signal to be received at the BS at the beginning of the UL slot, it could start transmitting before the GP occurs. In this manner, the UE_B will have a shorter DL transmission period and a longer associated GP, as compared to UE_A. UE_C behaves similarly to UE_B, but it will start transmitting even earlier due to its larger distance/larger propagation delay, as compared to the other UEs.

[0080] The BS will receive the three UL signals well aligned in time, based on each UE starting its UL transmission based on a UE-specific TA (timing advance offset). By using this approach, UE_A is not penalized by the presence of cell edge UEs with long propagation delay. UE_A can indeed maintain its short GP and increase its resource utilization and throughput. In general, this approach allows relaxing the dependence of the TDD radio frame configuration from the cell size. In the practice, a frame configuration featuring a GP duration which is necessary to cope only with a fraction of the cell radius can be selected, and a UE-specific GP and a length of a UE-specific DL transmission period may be determined for each UE, e.g., based on UE-BS propagation delay. Thus, in this manner, a greater use of resources may be provided via the per-UE GP and per-UE length of a DL transmission period.

[0081 ] According to one non-limiting example implementation, an operational mode of a TDD cell may use various techniques, including:

[0082] 1) The cell/BS selects a frame configuration with a GP duration necessary to cope with a fraction of the cell radius.

[0083] 2) When UEs are connecting to the BS, specific TA (timing advance offset) commands may be issued according to their estimated distance.

[0084] 3) DL resources are allocated to the UEs according to the distance- dependent time scheduling principle described above, e.g., where resources for a greater/longer DL transmission period may be allocated to a UE (e.g., UE_A) that is close to the BS (and associated with a shorter GP for such UE), whereas (less) resources for a shorter DL transmission period are allocated to a UE (e.g., UE_C) that is farther away from the BS (and associated with a longer GP for such UE). The BS may notify each UE of their respective TA and length of their DL transmission period and/or length of a UE- specific GP. For example, the U-specific GP may be based upon the UE-specific TA (timing advance offset), e.g., since both of these values may be based upon the UE-BS propagation delay for the UE. For example, to specify a length of the DL transmission period (and thereby indicate a length of an associated UE-specific GP), the BS may merely identify an ending point of the DL transmission period for the UE, e.g., since, at least in some cases/examples, all DL transmissions may start at the same point in time.

[0085] 4) In connected mode, the UEs are receiving their DL data and start their transmission according to the TA settings, such that their signal is received at the BS at the expected time.

[0086] Thus, in a LTE TDD cell (for example), a frame configuration with a GP duration coping with, or adjusted/determined based upon, the cell radius may be selected, and then the GP may be varied or adjusted, e.g., increased, for other UEs.

[0087] It should be noted that the illustrative example shown in FIG. 6 has been described with the starting point that a shorter GP is the default, or initial selection, which may then be increased for other UEs that are farther away from the BS. However, in other example implementations, the GP could be (initially) defined from the maximum cell range (e.g., as a maximum GP for UEs at the cell edge), and when connected to the network, UEs that are closer to the BS may use a shorter GP, and thus, the closer UEs may be configured to use a shorter and more efficient configuration of the radio resources that are residing within the potential switching region. Thus, a per-UE allocation or configuration of resources may be provided based on, for example, a per-UE GP and/or a per UE length of a DL transmission period. In an example implementation, the initial configuration or allocation or assignment of a GP to each UE may be based on either system information broadcast or UE autonomous decision based on measurements (for instance path loss estimations, or other measurements). In an example implementation, a granularity of the resource adjustment may be an integer amount of OFDM (orthogonal frequency division multiplex) symbols.

[0088] FIG. 7 is another example timing diagram illustrating transmission of signals for a wireless network corresponding to FIG. 2 in which a UE-specific downlink transmission period and an associated UE-specific guard period (GP) may be determined for each UE of the cell or network according to an example implementation. The UE- specific and variable length DL transmission periods and associated UE-specific GPs for each UE may be more easily seen in the timing diagram of FIG. 7. For example, from the perspective of the BS, a DL transmission period 710C and an associated GP 712C is determined by BS 134 for UE_C, e.g., based on the UE_C-BS propagation delay or distance. The receive period of time 714C may be the same length as the DL transmission period 7 IOC, although shifted in time due to the UEc-BS propagation delay. Similarly, a longer (as compared to UE_C) DL transmission period 710B, and associated shorter GP 712B may be determined by BS 134 for UE_B, e.g., based on the shorter propagation delay/distance for UE_B, as compared to UE_C. The receive period of time 714B (from UE perspective) may be the same length as the DL transmission period 710B, although shifted in time due to the UE_B-BS propagation delay. Likewise, an even longer (as compared to UE_B and UE_C) DL transmission period 710A, and associated shorter GP 712A may be determined by BS 134 for UE_A, e.g., based on the even shorter propagation delay/distance for UE_A, as compared to UE_B and UE_C. The receive period of time 714A (from UE perspective) may be the same length as the DL transmission period 71 OA, although shifted in time due to the UE_A-BS propagation delay. In this manner a per-UE (or UE-specific) DL transmission period and a per UE (or UE-specific) GP may be determined for each UE, and then used to transmit data or control information (or other signals) to each UE. These example techniques may allow a more efficient use of resources and may reduce excess idle periods for at least some UEs.

[0089] FIG. 8 is a block diagram of a wireless station (e.g., AP or user device) 800 according to an example implementation. The wireless station 800 may include, for example, one or two RF (radio frequency) or wireless transceivers 802A, 802B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The wireless station also includes a processor or control unit/entity (controller) 804 to execute instructions or software and control transmission and receptions of signals, and a memory 806 to store data and/or instructions.

[0090] Processor 804 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 804, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 802 (802A or 802B). Processor 804 may control transmission of signals or messages over a wireless network, and may control the reception of signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver 802, for example). Processor 804 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 804 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 804 and transceiver 802 together may be considered as a wireless transmitter/receiver system, for example.

[0091] In addition, referring to FIG. 8, a controller (or processor) 808 may execute software and instructions, and may provide overall control for the station 800, and may provide control for other systems not shown in FIG. 8, such as controlling input/output devices (e.g., display, keypad), and/or may execute software for one or more applications that may be provided on wireless station 800, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

[0092] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 804, or other controller or processor, performing one or more of the functions or tasks described above.

[0093] According to another example implementation, RF or wireless

transceiver(s) 802A/802B may receive signals or data and/or transmit or send signals or data. Processor 804 (and possibly transceivers 802A/802B) may control the RF or wireless transceiver 802A or 802B to receive, send, broadcast or transmit signals or data.

[0094] The embodiments are not, however, restricted to the system that is given as an example, but a person skilled in the art may apply the solution to other communication systems. Another example of a suitable communications system is the 5G concept. It is assumed that network architecture in 5G will be quite similar to that of the LTE-advanced. 5G is likely to use multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0095] It should be appreciated that future networks will most probably utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations may be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0096] Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Implementations may implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. Implementations may also be provided on a computer readable medium or computer readable storage medium, which may be a non-transitory medium. Implementations of the various techniques may also include implementations provided via transitory signals or media, and/or programs and/or software implementations that are downloadable via the Internet or other network(s), either wired networks and/or wireless networks. In addition, implementations may be provided via machine type

communications (MTC), and also via an Internet of Things (IOT).

[0097] The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

[0098] Furthermore, implementations of the various techniques described herein may use a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers,...) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electiOnics transported by humans or animals. The rise in popularity of smartphones has increased interest in the area of mobile cyber-physical systems.

Therefore, various implementations of techniques described herein may be provided via one or more of these technologies.

[0099] A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit or part of it suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[00100] Method steps may be performed by one or more programmable processors executing a computer program or computer program portions to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[00101 ] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer, chip or chipset. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[00102] To provide for interaction with a user, implementations may be

implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a user interface, such as a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[00103] Implementations may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[00104] While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method comprising:

receiving, by a base station, signals from a user device;

determining, by the base station, a length of a user device -specific downlink transmission period for transmitting from the base station to the user device;

transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

2. The method of claim 1 wherein the determining, by the base station, a length of a user device-specific downlink transmission period for the user device also determines a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

3. The method of claim 2 wherein, for the user device, the length of the user device-specific downlink transmission period plus the length of the associated guard period is a fixed period of time, such that a greater length of the user device- specific downlink transmission period provides a shorter associated guard period, and wherein a shorter length of the user device-specific downlink transmission period provides a longer associated guard period for the user device.

4. The method of claim 1 wherein the determining comprises:

determining, by the base station, an ending point of a user device-specific downlink transmission period for the user device, wherein a starting point for the user device-specific downlink transmission period for the user device is fixed.

5. The method of claim 1 wherein the determining comprises:

determining, by the base station, a propagation delay between the user device and the base station based on the signals received from the user device; and

determining the length of the user device-specific downlink transmission period for the user device based on the propagation delay.

6. The method of claim 5 :

wherein a shorter propagation delay between the user device and the base station provides for a longer user device-specific downlink transmission period and a shorter associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device; and

wherein a longer propagation delay between the user device and the base station provides for a shorter user device-specific downlink transmission period and a longer associated guard period between an end of the downlink transmission period and an uplink transmission period for the user device.

7. The method of claim 1 wherein the determining comprises:

determining, by the base station based on the received signals, a timing advance offset for the user device;

determining a user device-specific downlink transmission period for the user device based on the timing advance offset for the user device.

8. The method of claim 1 and further comprising:

sending, from the base station to the user device, a message indicating the user device- specific downlink transmission period for the user device.

9. The method of claim 1, wherein the method comprises:

receiving, by a base station, signals from a first user device and from a second user device;

determining, by the base station, a first propagation delay between the first user device and the base station;

determining, by the base station, a second propagation delay between the second user device and the base station;

determining, by the base station based on the first propagation delay, a length of a first user device-specific downlink transmission period for transmitting from the base station to the first user device;

determining, by the base station based on the second propagation delay, a length of a second user device-specific downlink transmission period for transmitting from the base station to the second user device; providing, by the base station to the first user device, an indication of the length of the first user device-specific downlink transmission period; and

providing, by the base station to the second user device, an indication of the length of the second user device-specific downlink transmission period.

10. The method of claim 1 wherein the determining comprises:

determining, by the base station, a length of a user device-specific downlink transmission period for the user device based on at least one of the following:

a propagation delay between the user device and the base station;

a location of the user device relative to the base station;

a distance between the user device and the base station; and

a received signal strength or received power for a signal receive by the base station from the user device.

11. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

receive, by a base station, signals from a user device;

determine, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and

transmit, by the base station to the user device, downlink signals during the user device- specific downlink transmission period.

12. A computer program product, the computer program product comprising a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising:

receiving, by a base station, signals from a user device; and

determining, by the base station, a length of a user device-specific downlink transmission period for transmitting from the base station to the user device; and transmitting, by the base station to the user device, downlink signals during the user device-specific downlink transmission period.

13. A method comprising:

receiving, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device; and

receiving, by the user device from the base station, signals during the user device- specific downlink transmission period for the user device.

14. The method of claim 13 wherein the receiving, by the user device from the base station, an indication of a user device- specific downlink transmission period comprises:

receiving, by the user device from the base station, an ending point of a user device- specific downlink transmission period for the user device.

15. The method of claim 13 and further comprising:

sending signals from the user device to the base station.

16. The method of claim 15 wherein the sending comprises at least one of the following:

sending, from the user device to the base station, a random access request;

sending, from the user device to the base station, uplink reference signals; and

sending, from the user device to the base station, uplink data.

17. The method of claim 13 wherein the length of the user device-specific downlink transmission period for the user device also determines a length of an associated guard period between an end of the downlink transmission period and a beginning of an uplink transmission period for the user device.

18. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:

receive, by a user device from a base station, an indication of a user device-specific downlink transmission period for the user device; and

receive, by the user device from the base station, signals during the user device-specific downlink transmission period for the user device.