220 research outputs found
Capacity Analysis of LTE-Advanced HetNets with Reduced Power Subframes and Range Expansion
The time domain inter-cell interference coordination techniques specified in
LTE Rel. 10 standard improves the throughput of picocell-edge users by
protecting them from macrocell interference. On the other hand, it also
degrades the aggregate capacity in macrocell because the macro base station
(MBS) does not transmit data during certain subframes known as almost blank
subframes. The MBS data transmission using reduced power subframes was
standardized in LTE Rel. 11, which can improve the capacity in macrocell while
not causing high interference to the nearby picocells. In order to get maximum
benefit from the reduced power subframes, setting the key system parameters,
such as the amount of power reduction, carries critical importance. Using
stochastic geometry, this paper lays down a theoretical foundation for the
performance evaluation of heterogeneous networks with reduced power subframes
and range expansion bias. The analytic expressions for average capacity and 5th
percentile throughput are derived as a function of transmit powers, node
densities, and interference coordination parameters in a heterogeneous network
scenario, and are validated through Monte Carlo simulations. Joint optimization
of range expansion bias, power reduction factor, scheduling thresholds, and
duty cycle of reduced power subframes are performed to study the trade-offs
between aggregate capacity of a cell and fairness among the users. To validate
our analysis, we also compare the stochastic geometry based theoretical results
with the real MBS deployment (in the city of London) and the hexagonal-grid
model. Our analysis shows that with optimum parameter settings, the LTE Rel. 11
with reduced power subframes can provide substantially better performance than
the LTE Rel. 10 with almost blank subframes, in terms of both aggregate
capacity and fairness.Comment: Submitted to EURASIP Journal on Wireless Communications and
Networking (JWCN
Enhanced Inter-Cell Interference Coordination Challenges in Heterogeneous Networks
3GPP LTE-Advanced has started a new study item to investigate Heterogeneous
Network (HetNet) deployments as a cost effective way to deal with the
unrelenting traffic demand. HetNets consist of a mix of macrocells, remote
radio heads, and low-power nodes such as picocells, femtocells, and relays.
Leveraging network topology, increasing the proximity between the access
network and the end-users, has the potential to provide the next significant
performance leap in wireless networks, improving spatial spectrum reuse and
enhancing indoor coverage. Nevertheless, deployment of a large number of small
cells overlaying the macrocells is not without new technical challenges. In
this article, we present the concept of heterogeneous networks and also
describe the major technical challenges associated with such network
architecture. We focus in particular on the standardization activities within
the 3GPP related to enhanced inter-cell interference coordination.Comment: 12 pages, 4 figures, 2 table
A distributed power-saving framework for LTE Het-Nets exploiting Almost Blank Subframes
Almost Blank Subframes (ABS) have been defined in LTE as a means to coordinate transmissions in heterogeneous
networks (HetNets), composed of macro and micro eNodeBs: the macro issues ABS periods, and refrains from transmitting during ABSs, thus creating interference-free subframes for the micros. Micros report their capacity demands to the macro via the X2 interface, and the latter provisions the ABS period accordingly. Existing algorithms for ABS provisioning usually share resources
proportionally among HetNet nodes in a long-term perspective (e.g., based on traffic forecast). We argue instead that this mechanism can be exploited to save power in the HetNet: in fact, during ABSs, the macro consumes less power, since it only transmits pilot signals. Dually, the micros may inhibit data transmission themselves in some subframes, and optimally decide when to do this based on knowledge of the ABS period. This allows us to define a power saving framework that works in the short term, modifying the ABS pattern at the fastest possible pace, serving the HetNet traffic at reduced power cost. Our framework is designed using only standard signaling. Simulations show that the algorithm consumes less power than its competitors, especially at low loads, and improves the UE QoS
Coverage Analysis of Reduced Power Subframes Applied in Heterogeneous Networks with Subframe Misalignment Interference
IEEE In heterogeneous networks (HetNets), to reduce the interference to users in Cell Range Expansion (CRE) areas of small cells, Reduced Power Subframes (RPSs) are used by macro base stations (BSs) to serve their center region users. CRE users can receive full power subframes (FPSs) from small-cell BSs in the same time slots as RPSs. However, it is difficult to maintain strict subframe alignment (SA) between neighbouring cells. Subframe misalignment (SM) between RPSs and FPSs transmitted by neighbouring macro BSs and small-cell BSs may degrade the coverage performance for macrocell center and small-cell CRE users. With existing time synchronization techniques used in HetNets, the SM offsets are actually upper-bounded. In this letter, we propose a novel SM model for a two-tier HetNet adopting RPSs with SM offsets restricted within a subframe duration, and analyse the coverage probability under the effects of RPSs and SM based on stochastic geometry. The results show that the strict SA requirement can be relaxed by up to 20% of subframe duration with below 5% coverage loss
Hierarchical Radio Resource Optimization for Heterogeneous Networks with Enhanced Inter-cell Interference Coordination (eICIC)
Interference is a major performance bottleneck in Heterogeneous Network
(HetNet) due to its multi-tier topological structure. We propose almost blank
resource block (ABRB) for interference control in HetNet. When an ABRB is
scheduled in a macro BS, a resource block (RB) with blank payload is
transmitted and this eliminates the interference from this macro BS to the pico
BSs. We study a two timescale hierarchical radio resource management (RRM)
scheme for HetNet with dynamic ABRB control. The long term controls, such as
dynamic ABRB, are adaptive to the large scale fading at a RRM server for
co-Tier and cross-Tier interference control. The short term control (user
scheduling) is adaptive to the local channel state information within each BS
to exploit the multi-user diversity. The two timescale optimization problem is
challenging due to the exponentially large solution space. We exploit the
sparsity in the interference graph of the HetNet topology and derive structural
properties for the optimal ABRB control. Based on that, we propose a two
timescale alternative optimization solution for the user scheduling and ABRB
control. The solution has low complexity and is asymptotically optimal at high
SNR. Simulations show that the proposed solution has significant gain over
various baselines.Comment: 14 pages, 8 figure
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