Patent Application
20120190372
The present invention relates generally to the field of wireless communications. More particularly, the present invention relates to facilitating handoff operations in a wireless communication system.
In cellular networks, radio nodes, also sometimes referred to as base stations, access points, cells, Node Bs, eNodeBs, and the like, are normally installed and commissioned after a careful upfront planning and survey process, which is followed by extensive post installation optimization efforts to maximize the network performance. Such optimization efforts usually involve a considerable amount of manual intervention that could include “drive testing” using specialized measurement devices to collect data on network performance at a variety of geographical locations. This data is then post-processed and analyzed to effect optimization steps including power adjustments, antenna tilt adjustments and the like.
Such prior planning, installation and post-installation efforts can become cost prohibitive for networks that cover complicated physical spaces spanning multiple floors of a building, including elevator shafts, stairwells, atria and meeting rooms. In addition, expensive planning, installation and post-installation procedures often do not make business sense for small-cell (e.g., local area) networks that are installed and operated relatively inexpensively. In particular, the cost of installation procedures may be prohibitive in enterprise networks that are described herein, as well as applications that relate to high-density capacity enhancements of a downtown city square and ad-hoc deployment of a cellular network such as in military applications. Nevertheless, proper configuration and optimization of an enterprise network is important for enabling efficient utilization of network resources, as well as conducting operations such as handoffs between and within the networks.
The disclosed embodiments relate to methods, devices, and computer program products that facilitate various handoff operations by examining radio frequency (RF) and air-interface issues that are likely to be encountered in user equipment (UE) handovers between a macro network and an enterprise network. In one embodiment, the dynamics of RF signal strength and interference values during handover are examined. The handover operations may be carried out in small-cells for outdoor capacity in-fill within the umbrella of a macro network.
One aspect of the disclosed embodiments relates to a method for managing uplink signal quality at a radio node and at a macrocell and/or external cell. The method includes determining a first transmit power associated with a radio node of a small-cell radio access network and a second transmit power associated with a macrocell and/or an external cell. The method further includes providing a desense value associated with an uplink of the radio node of the small-cell radio access network, wherein the desense value in association with the first and second transmit powers enables balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the macrocell and/or external cell in relation to a downlink of the radio node of the small cell radio access network and a downlink of the macrocell and/or external cell, thereby managing uplink signal quality at the radio node of the small-cell radio access network and at the macrocell and/or external cell.
Another aspect of the disclosed embodiments relates to a device that comprises a processor and a memory that comprises processor executable code. The processor executable code, when executed by the processor, configures the device to a first transmit power associated with a radio node of a small-cell radio access network and a second transmit power associated with a macrocell. The processor executable code, when executed by the processor, further configures the device to provide a desense value associated with an uplink of the radio node of the small-cell radio access network, wherein the desense value in association with the first and second transmit powers enables balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the macrocell and/or external cell in relation to a downlink of the radio node of the small cell radio access network and a downlink of the macrocell and/or external cell, thereby managing uplink signal quality at the radio node of the small-cell radio access network and at the macrocell and/or external cell.
Another aspect of the disclosed embodiments relates to a computer program product, embodied on a computer non-transitory readable medium. The computer readable medium comprises program code for determining a first transmit power associated with a radio node of a small-cell radio access network and a second transmit power associated with a macrocell. The computer readable medium further comprises program code for providing a desense value associated with an uplink of the radio node of the small-cell radio access network, wherein the desense value in association with the first and second transmit powers enables balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the macrocell and/or external cell in relation to a downlink of the radio node of the small cell radio access network and a downlink of the macrocell and/or external cell, thereby managing uplink signal quality at the radio node of the small-cell radio access network and at the macrocell and/or external cell.
In one embodiment, the desense value is determined in accordance with a transmit power of the radio node of the small-cell radio access network, a transmit power of the macrocell and a noise level associated with the macrocell.
One aspect of the disclosed embodiments relates to another method for managing uplink signal quality at a first radio node and at a second radio node. The method includes determining a first transmit power associated with a first radio node of a small-cell radio access network and a second transmit power associated with a second radio node of the small-cell radio access network. The method also includes determining a first desense value associated with an uplink of the first radio node. The method further includes determining a second desense value associated with an uplink of the second radio node, wherein the first and the second desense values enable balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the second radio node in relation to a downlink of the first radio node and a downlink of the second radio node, thereby managing uplink signal quality at the first radio node and the second radio node.
In one embodiment, the first desense value is determined in accordance with a constant desense value, a maximum transmit power of all radio node of the small-cell radio access network and a transmit power of the first radio node. In another embodiment, the second desense value is determined in accordance with a constant desense value, a maximum transmit power of all radio node of the small-cell radio access network and a transmit power of the second radio node.
One aspect of the disclosed embodiments relates to a device that comprises a processor and a memory comprising processor executable code. The processor executable code, when executed by the processor, configures the device to determine a first transmit power associated with a first radio node of a small-cell radio access network and a second transmit power associated with a second radio node of the small-cell radio access network. The processor executable code, when executed by the processor, further configures the device to determine a first desense value associated with the uplink of the first radio node; and determine a second desense value associated with an uplink of the second radio node, wherein the first and the second desense values enable balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the second radio node in relation to a downlink of the first radio node and a downlink of the second radio node, thereby managing uplink signal quality at the first radio node and the second radio node.
Another aspect of the disclosed embodiments relates to a computer program product, embodied on a computer readable medium. The computer program product comprises program code for determining a first transmit power associated with a first radio node of a small-cell radio access network and a second transmit power associated with a second radio node of the small-cell radio access network. The computer program product further comprises program code for determining a first desense value associated with the uplink of the first radio node; and program code for determining a second desense value associated with an uplink of the second radio node, wherein the first and the second desense values enable balancing of a first signal to noise-plus-interference ratio associated with an uplink of the small-cell radio access network and a second signal to noise-plus-interference ratio associated with an uplink of the second radio node in relation to a downlink of the first radio node and a downlink of the second radio node, thereby managing uplink signal quality at the first radio node and the second radio node.
These and other advantages and features of various embodiments of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.
Embodiments of the invention are described by referring to the attached drawings, in which:
In the following description, for purposes of explanation and not limitation, details and descriptions are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions.
Additionally, in the subject description, the word “exemplary” is used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word exemplary is intended to present concepts in a concrete manner. Further, some of the disclosed embodiments are described in the context of an enterprise network. However, it should be understood that the disclosed concepts are equally applicable to other types of networks.
The disclosed embodiments facilitate various types of handoff operations. A handoff, which is sometimes referred to as a handover, refers to the transfer of an ongoing communication session (e.g., a voice or data session) from one radio link to another radio link. The transfer of the on-going session can be to another network (e.g., to a network with a different radio access technology (RAT) or an inter-RAT handoff), to another cell, to another sector of the same cell, to another frequency within the same cell and the like. Additionally, or alternatively, the various handoff scenarios may be described in terms of inter-frequency and intra-frequency handoff operations. Inter-frequency handoff refers to adding a radio link for service to the user equipment on a different logical entity which uses a different channel frequency, such as a neighboring cell operating on a different frequency. Inter-frequency handoff can, but does not necessarily, include terminating the radio link on the source cell (i.e., a hard handoff that is described in sections that follow). Intra-frequency handoff refers to adding a radio link on a different logical entity which uses the same channel frequency. Further, the term “cell” may be construed in different ways. For example, a cell can be considered a logical entity that manages a single radio channel (i.e., the typical definition in the context of Universal Mobile Telecommunications System (UMTS)). In other examples, a cell may be considered a logical entity that manages multiple radio channels, usually on different frequencies. In still other examples, a cell may can be construed as a logical entity that manages multiple radio channels, on the same or different frequencies, that have been sectorized. In other scenarios, a cell can be considered a physical area covered adequately by RF energy from a particular sector of a physical base station installation, which can include just one RF channel or multiple RF channels. In yet other examples, a cell can be construed as a physical area covered adequately by RF energy from all sectors of a physical base station installation, which can also include one or multiple RF channels.
The disclosed embodiments also facilitate different types of handoffs that are known as hard, soft and softer handoffs. In a hard handoff, the connection to the existing radio link is broken before the connection to the new radio link is established. In a soft handoff, the existing radio link is retained and used in parallel with one or more newly acquired radio links of the target cell(s). The simultaneous connections in a soft handoff may be for a brief or substantial period of time. A softer handoff, which is used in Universal Mobile Telecommunications System (UMTS), is a special case of a soft handoff, where the radio links that are used in parallel belong to the same Node B.
A handoff can be initiated for a variety of reasons. For example, a user equipment that moves to another geographical area, which is outside of the coverage area of its existing cell, may initiate a handoff to avoid termination of the on-going session. In another example, a handoff to another cell may be initiated to free up resources at an existing cell. In yet another example, a handoff is used to improve interference from other channels. In order to initiate a handoff, the user equipment must be aware of potential target cells (i.e., neighboring radio nodes) that are likely to accommodate the handoff. The information regarding the neighboring radio nodes can be provided in a listing that is often referred to a neighbor list. In the context of an enterprise network, neighbor radio nodes may include both radio nodes that are internal to the enterprise network and the ones that operate outside of the enterprise network.
The exemplary block diagram that is shown in
It should be noted that while the exemplary radio networks that are depicted in
It should be also noted that in some embodiments a handoff operation may be more specifically described by using the terms “hand-in” and “hand-out.” A hand-in operation is associated with receiving an on-going session that is transferred into the current network from an external network, while a hand-out operation is associated with the transfer of an on-going session out from the current network to an external network.
The following is a listing of signal, noise and interference quantities that may be used to describe the handoff dynamics that are described in connection with the disclosed embodiments.
In the disclosed embodiments, the listed quantities are presented in logarithmic domain to enable a linear analysis, thereby facilitating the understanding of the underlying concepts. However, it is understood that the disclosed embodiments can be similarly developed in a non-logarithmic domain.
One of the aspects of the disclosed embodiments relates to uplink de-sense mechanisms within the internal network and signal transients during soft-handover. In some embodiments, an enterprise network (such as the network depicted in
The disclosed embodiments mitigate this problem by injecting white noise to desensitize the receiver. Injecting noise with a variance of σd2 is equivalent to increasing the uplink path loss between the UE and the radio node by the same amount. Therefore, a careful choice of σd2 ensures that a UE is always in power-controllable range, preventing it from railing against its minimum transmit power PT,minUL. This injected noise is hereinafter referred to as “desense” for convenience.
It is important to note that the downlink path loss is not affected in any way by the addition of de-sense noise. Also note that UE's are not expected to be power limited in small-cell networks, such as the E-RAN that is depicted in
σd,i2=σd2+(maxj(PT,S,j)−PT,S,i) (Eq. 1).
In Equation (1), maxj(PT,S,j) represents the maximum transmit power across all radio nodes of the small-cell radio access network. The effective noise floor for a radio node of the small-cell radio access network is then given by:
N
S,i
eff=10·log10(lin(NS,i)+lin(σd,i2)) (Eq. 1a).
In Equation (1a), lin(x)=100.1(x) represents conversion of a logarithmic quantity to a linear quantity. Since the additive de-sense noise is typically much greater than the noise floor (i.e., σd,i2>>NS,i), the effective noise is essentially the same as the injected de-sense value, as expressed by the following:
N
S,i
eff≈σd,i2 (Eq. 1b).
Apart from serving to control interference from a near user, the injected de-sense may be used to balance uplinks in a handover situation. One aspect of the disclosed embodiments relates to signal transients during a handoff within the small-cell radio access network. While the following operations are described in the context of a soft handoff, it is understood that the disclosed embodiments are also applicable to other types of handoff, such a hard handoffs.
In the following, downlink signal dynamics with reference to
P
R,S,i
=P
T,S,i
+G
i
−P
L,i′
for i=1,2 (Eq. 2).
The difference in the downlink received CPICH powers is:
(PR,S,1−PR,S,2)=(PT,S,1−PT,S,2)+(G1−G2)−(PL,1−PL,2) (Eq. 3).
At the ideal handover point i.e., assuming no hysteresis or bias and zero signaling delay, the received CPICH powers are equal. This is because the measurements of CPICH related quantities (RSCP or Ec/No) are typically used as handoff decision triggers. This naturally implies that the ideal handoff point is reached when the difference in path losses is equal to the difference in CPICH transmit powers. In other words, the ideal handoff is reached when:
(PT,S,1−PT,S,2)+(G1−G2)=(PL,1−PL,2) (Eq. 4).
With reference to
P
R,S,i
UL
=P
T
UL
+G
i
−P
L,i′ for i=1,2 (Eq. 5).
The quantity of interest in the uplink is the signal-to-noise plus interference ratio (SIR), which determines power control behavior and session stability. The following analysis assumes the calculation of SIR ratios at the chip-level rather than the symbol level, effectively ignoring the spreading factor of the waveform and the associated processing gain. On a particular radio node ‘i’, of the small-cell radio access network, the SIR is given by Equations (1a) and 1(b). Therefore, the SIR is given by the ratio of the received signal power to the sum of thermal and injected desense noise. Assuming that the sum of thermal and injected desense noise can be approximated by just the de-sense noise, SIR for radio node i can be determined as:
SIR
i
=P
R,S,i
UL−σd,i2 (Eq. 6).
The difference in the signal-to-noise ratios is given by:
(SIR1−SIR2)=(G1−G2)+(PL,2−PL,1)−(σd,12−σd,22) (Eq. 7).
Since the difference in path loss ratios at the ideal handover point is equal to the difference in downlink CPICH transmit powers adjusted by the antenna gains (see Equation (4)), Equation (7) may be recast as:
(SIR1−SIR2)=(PT,S,2−PT,S,1)−(σd,12−σd,22) (Eq. 8).
By suitably choosing the variance of injected noise to be related to the transmit power, as described in Equation (1), and substituting this value in Equation (8), an uplink SIR balance at the ideal handover point can be achieved. Therefore, both downlinks and uplinks are balanced at this point. From a practical perspective, the above-described balancing of the downlinks and uplinks is straightforward with a centralized architecture due to the computation of Equation (1). In a distributed architecture with direct connections between the radio nodes, the above-described operations may be carried out through cooperation of the multiple nodes.
Another aspect of the disclosed embodiments relates signal dynamics in handoffs between a macrocell (e.g., a cell external to the small-cell radio network) and a radio node of a small-cell radio access network, such as the exemplary E-RAN that is depicted in
Assuming, once again, that the ideal handoff point as that location at which the downlink received CPICH measurements are equal, the following relationship, analogous to the one expressed by Equation (4), can be developed for downlink:
(PT,M−PT,S)+(GM−GS)=(PL,M−PL,S) (Eq. 9).
In Equation (9), the subscripts M and S correspond to the macrocell and the small-cell radio access network, respectively. It is uncommon for macrocells to use any level of desense, as the goal is often to maximize link budget, not to compromise it. Therefore, the noise floor at the macrocellis assumed to be NM and σd,m2 is assumed to be zero. Examination of the uplink SIR at this point, in line with the analysis discussed in connection with Equations (5)-(8), yields the following equation:
(SIRM−SIRS)=(PT,S−PT,M)−(NM−σd,S2) (Eq. 10).
It is evident from Equation (10) that uplink SIRS at the macrocell and the radio node of the small-cell radio access network may be balanced at the ideal handoff point with an appropriate choice of the desense noise level, σd,S2, at the radio node of the small-cell radio access network, according to the following equation:
σd,S2=(PT,M−PT,S)+NM (Eq. 11).
It is evident from Equation (11), that through the exchange of information, such as NM between the small-cell radio network and the macrocell, a proper value of the desense can be determined to balance the SIRs for handoff purposes. Furthermore, the change in desense level due to knowledge of the macro network, as compared to the internal value computed in the small-cell radio access network (i.e., using Equation (1)), may be applied uniformly through the small-cell radio access network due to the small-cell RF management suite that resides, for example, on a centralized controller.
In still other embodiments, the macro network could specifically inform the small-cell network of an impending handover into the small-cell network so that the de-sense value can be increased only when necessary to facilitate link balancing upon hand-in. This could be done by slowly ramping de-sense across the small-cell radio network so as to not de-stabilize existing connections and allowing power control loops to keep up. In one example, the de-sense value is lowered again following the completion of the hand-in operation.
In other embodiments, handoff operations between adjacent small-cell networks can be facilitated through operations that are similar to those discussed in connection with
It is understood that the various embodiments of the present invention may be implemented individually, or collectively, in devices comprised of various hardware and/or software modules and components. These devices, for example, may comprise a processor, a memory unit, an interface that are communicatively connected to each other, and may range from desktop and/or laptop computers, to consumer electronic devices such as media players, mobile devices and the like. For example,
The various components or sub-components within each module of the disclosed embodiments may be implemented in software, hardware, firmware. The connectivity between the modules and/or components within the modules may be provided using any one of the connectivity methods and media that is known in the art, including, but not limited to, communications over the Internet, wired, or wireless networks using the appropriate protocols.
Various embodiments described herein are described in the general context of methods or processes, such as the processes described in
The foregoing description of embodiments has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments. For example, the disclosed embodiments are equally applicable to networks that utilize different communication technologies, including but not limited to UMTS (including R99 and all high-speed packet access (HSPA) variants), as well as LTE, WiMAX, GSM and the like. The embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments and its practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.
| Number | Date | Country | |
|---|---|---|---|
| 61435745 | Jan 2011 | US |
