1- RAN Enhancements for Advanced MBMS
Transcript of 1- RAN Enhancements for Advanced MBMS
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
1/7
Contribution to the WWRF17 Meeting
1 WG or SIG to which this Contribution is submitted:
WG4
2 State which of the categories a) f) on the front page of the CfC thisContribution is addressing:
Identifying new research areas
3 Title of research item
RAN Enhancements for Advanced Multimedia Broadcasting and Multicasting Services
4 Contact details of author/submitter
Rainer Hoeckmann
University of Applied Sciences Osnabrueck
Postfach 1940
49009 Osnabrueck
Phone: +49 541 969 3800
5 Subject area (WG/SIG and subtopic (as of CfC) where appropriate)
WG4 New Air Interfaces, Relay based Systems and Smart Antennas
Several subtopics will be covered
6 Relevance of the topic to the above subject area
The IST project C-MOBILE (Advanced MBMS for the Future Mobile World) intends to present itsidentified research directions for RAN.
7 Preferred presentation form:
speech
8 Abstract
see below
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
2/7
Page 2 (7)
2
AbstractMobile multimedia services like goal notification
for football fans by Multimedia Messaging Service (one club =
one channel) and mobile television require efficient technologies
in order to distribute multimedia contents simultaneously to
large mobile user groups. UMTS (Universal Mobile
Telecommunications System) Release 6 has standardised
MBMS (Multimedia Broadcast and Multicast Services) for the
first time. This paper discusses issues for evolving mobile
broadcast services with higher bandwidth and more flexibility.
The document discusses the future research directions
concerning RAN enhancements for the provision of advanced
Multimedia Broadcast Multicast Services. A particular focus is
given on the RAN enhancements addressed in the European
project C-MOBILE.1
Index TermsImproved MBMS Support, Research
Directions, RAN Evolution
I. INTRODUCTION
Mobile multimedia services like goal notification for
football fans by Multimedia Messaging Service (one club =
one channel) and mobile television require efficient
technologies in order to distribute multimedia contents
simultaneously to large mobile user groups [1][2]. UMTS
(Universal Mobile Telecommunications System) Release 6
has standardised MBMS (Multimedia Broadcast and
Multicast Services) for the first time [3][4]. The C-MOBILE
project deals with enhancements to MBMS radio and core
network capabilities in future wireless cellular networks,
mobile broadcast service infrastructure capabilities andconvergent architecture. This paper is based on the first
deliverable [5] by the Work Package 3 RAN
Enhancements of C-MOBILE [6].
In section II, the status in standardization is reviewed and
specific RAN enhancements are classified.
Section III summarizes concepts and technologies
currently under discussion in standardization and section IV
concludes the discussion.
II. TECHNOLOGIES AND CONCEPTS FOR 3GPPEVOLUTION
A. WCDMA based MBMS Evolution in 3GPPWith the 3GPP Release 99 and Release 5 standards being
This contribution is the result of work done as part of the IST C-
MOBILE project (IST-2005-27423) [6].
frozen, enhancements can be applied on the receiver side or
on certain non-standardized algorithms. Relevant techniques
are:
Interference cancellation (IC) in order to mitigate inter-
cell and/or intra-cell interference, as it is interesting for
HSDPA Release 5. Adaptive IC scheme that allow foran intelligent trading of receiver complexity vs.
performance are worth to be studied.
Receive diversity for an improved coverage and/or in
order to reduce the transmit power at the base station.
Receive diversity schemes designed for interference
nulling. This advanced technique does not optimize for
SNR (signal-to-noise ratio) via maximum-ratio
combining, but for the SINR (signal-to-interference
and noise ratio).
Improved HSDPA scheduling, traffic-channel
switching, RRM. Since the standard does not specify
these algorithms, more sophisticated proprietarysolutions can be applied
C-MOBILE will consider various possibilities to enhance
the MBMS Release 6 performance, and consider concepts
and technologies already listed in the Release 7 Study Item
MBMS Release 6 Evolution, comprising techniques such
as:
Selection and Soft Combining.
Advanced counting procedures for a more efficient
utilisation of system resources, in order to avoid
congestion resulting from uncontrolled terminal
feedback. Better MBMS mobility support and optimizations for
MBMS reception during cell change.
Improved ptp-ptm (point-to-point vs. point-to-
multipoint) switching, for optimized overall cell
throughput as well as to guarantee a certain QoS at the
UE.
Optimizations for scenarios where the RNC does not
know whether the UE supports the MBMS ptm
reception in the CELL_DCH state.
Provision of an MBMS dual receiver to permit joint
ptp and ptm reception, or the handling of MBMS
services on different frequencies. The study of MBMS on the HSDPA transport channel.
Finally, broadband MBMS support based on MC-
WCDMA will be considered.
RAN Enhancements for Advanced Multimedia
Broadcasting and Multicasting Services
E. Alexandri
1
, J. Antoniou
2
, T. Clessienne
1
, A. Correia
3
, R. Dinis
3
, E. Hepsaydir
5
,R. Hckmann4, H. Schotten
6, C. Sgraja
6, R. Tnjes
4, N. Souto
3, S. Wendt
1
1France Telecom,
2Univ. of Cyprus,
3ADETTI,
4Univ. Appl. Sci. Osnabrck,
5Hutchison 3G,
6Qualcomm
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
3/7
Page 3 (7)
3
There are various scenarios where MBMS services might
be delivered on unicast bearers. It is expected that there will
be an HSPA evolution, and that HSDPA+ bearers might
be used for MBMS service support.
B. LTE based MBMS evolution in 3GPPThe overall target of the 3GPP long-term evolution (LTE)
of 3G is to arrive at an evolved radio access technology that
can provide service performance on a par with current fixed
line access. As it is generally assumed that there will be a
convergence towards the use of Internet Protocol (IP)-based
protocols (i.e. all services in the future will be a carried on
top of IP), the focus of this evolution should be on
enhancements for packet-based services.
An OFDMA air interface has been selected for LTE. One
of the LTE requirements is to deliver enhanced MBMS,
where C-MOBILE will study and make necessary proposals
to 3GPP for LTE.
In the LTE architecture as it was proposed, the network
nodes GGSN, SGSN, and RNC will be merged into a single
central node, the Access Core Gateway (ACGW). The
ACGW terminates the control and user planes for the user
equipment (UE) and handles the core network functions as
they are provided by GGSN and SGSN in Release 6.
Link LayerLTE suggests a new link layer concept:
packet-centric link layer. The concept foresees two Layer-2
ARQ protocols, the RLC protocol which contains ARQ
functionality, and the hybrid ARQ (HARQ) protocol
embedded in the medium access control (MAC) layer and
operating between the base station and the UE. This is
expected to allow for more efficient scheduling decisions.
DownlinkOFDM. In OFDM-SFNs (single frequency
networks), the signal from all base stations will appear as
multi-path propagation and thus implicitly be exploited by
the OFDM receiver. In addition, frequency domain
adaptation is made possible through the use of OFDM and
can achieve large performance gains in cases where the
channel varies significantly over the system bandwidth.
Information about the downlink channel quality obtained
through feedback from the terminals, in order to
appropriately select the output power level, channel coding
rate, and modulation scheme by the scheduler.
UplinkSingle-Carrier FDMA. For uplink transmissions,
an important requirement is to allow for power-efficient
user-terminal transmissions by lowering the PAPR (peak-to-
average power ratio) in order to maximize coverage. Single-
carrier FDMA with dynamic bandwidth is therefore
preferred. Slow power control, compensating for path loss
and shadow fading is sufficient as no near-far problem is
present due to the orthogonal uplink transmissions.
MIMO SolutionsTo fulfil the requirements on coverage,
capacity, and high data rates, various multi-antenna schemes
need to be supported as part of LTE. In addition, it is
necessary to consider multi-antenna technologies as a well-
integrated part of an evolved radio access rather than an
extension to the specification.
Since the deployment of LTE requires new spectrum,
some operators might not be in the position to migrate LTE
from the very beginning. Other operators already indicate
that they will deploy LTE in hotspots first and handover the
users to WCDMA in other areas. A third group plans to
deploy LTE from the very beginning with full coverage.
In addition, there are options to use currently unused
spectrum for stand-alone MBMS support that shall however
be closely tied to a 3G system. These MBMS solutions
could be deployed in parallel to any other deployment
strategy providing full or restricted coverage.
III. RANENHANCEMENT TECHNIQUES
A. Improved RRM1) Dynamic Service Area Definition & Resource
Allocation
The MBMS Service Area is defined as the area where
MBMS data of a specific MBMS session are transmitted.
The MBMS Service Area is statically configured in the RNC
in Release 6, and research is needed to investigate theadvantages of using dynamic MBMS Service Area definition
together with mechanisms to achieve this goal.
In addition, to improve the overall system capacity, an
MBMS service delivery into a handset can be scheduled
when the network is less loaded.
2) Improved Packet SchedulingHS-DSCH is currently used for unicast services due to its
point-to-point nature, but the rich features such as adaptive
coding and modulation (ACM), fast scheduling, hybrid ARQ
and short TTI, make the HS-DSCH a good candidate for
multicast services. Users belonging to the same MBMS
group will have the same H-RNTI (HS-DSCH Radio
Network Temporary Identifier). Further research has to
study and propose algorithms for the packet scheduler in the
base station defining how to use the CQI reported by the
MBMS UEs. The study should also quantify the benefit of
using MBMS on HS-DSCH.
Streaming is one of the most expected MBMS services. A
typical feature of streaming applications is that they do not
require as strict and small delay bounds as conversational
applications do. The use of a receiver buffer makes a
streaming application resistant against latencies. In order to
avoid under- and overflows and therewith packet loss, the
scheduler must have the information of the state of the
receivers buffers.
As the HSDPA-related MAC functionality resides in the
base station, fast per-TTI packet scheduling (PS) in
coherence with the instantaneous radio link quality is
possible.
Two types of fairness of the scheduler can be considered:
Fair Scheduling and Unfair Scheduling. A simple type of
channel non-adaptive scheduling, known to allocate the
access times fairly, is the Round Robin (RR) scheduler.
However, although the time allocation of RR is fair, the
performance is mostly not very encouraging in fading
environments. Improved schemes for efficient packet
scheduling are therefore of relevance.
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
4/7
Page 4 (7)
4
3) New Retransmission SchemesHybrid ARQ is well defined for unicast services. In the
case of multicasting, there could be many variants. Suppose
a frame is to be delivered to a number of users in a multicast
group. After the initial transmission, some users may have
successfully decoded the message, while the other users still
require retransmissions. Upon the reception of ACK/NACK
feedbacks, the base station will either schedule
retransmission for the NACK users or decide to stop the
transmission, since a majority of users have already got the
frame.
The first approach, i.e., the error free data delivery
required by the file download service, can be guaranteed by
unicast sessions to be set up at the end of the multicast
session for file repair.
4) Enhanced ptp-ptm SwitchingMBMS channel type switching is also possible as per
3GPP Release 6 of the standard. During an ongoing session,
the RNC can decide to switch from ptm to ptp per cell. As
usual the standard does not specify the parameters to be usedby the RNC to make this decision (it is worth highlighting
there may be ptm data delivery between BM-SC, SGSN,
GGSN and RNC, while ptp at the radio level).
Further investigations are needed for efficient mechanisms
to switch from ptp to ptm and vice-versa:
The RNC can set up a ptp (unicast) or ptm (multicast)
radio bearer depending on several parameters, such as
the number of the MBMS users in a cell. The number
of MBMS users per service and per cell can be worked
out through the MBMS Counting mechanism.
MBMS Counting relies on the MBMS Counting
Response message sent by the UEs, when they receivea request for counting.
If the UE is in idle mode, the RRC connection
establishment procedure will be used for counting
purposes, while if the UE is in connected mode the
Cell Update procedure will be used. Counting can be
even activated during an ongoing MBMS session. In
that case the procedure is called re-counting.
In order to avoid that a large number of UEs set up a
RRC connection or send Cell Up-date as a response
from the counting request, the UE is requested to
access the net-work randomly.
Further investigations concern the impact of different
channels for ptp and ptm modes such as HS-DSCH
(ptp) and DSCH (ptm). If a ptm bearer is chosen, then
the transport channel to be used will be FACH. If a ptp
bearer is selected, then the transport channel which can
be used is either DCH or HS-DSCH.
Also, the role of power in the switching decision
between ptp and ptm cell modes will be studied, in the
case that power is an efficient metric such as, for
example, when switching between DCH and FACH.
5) Improved MBMS Counting3GPP specifications address the issue of ptp-ptm
switching by means of the MBMS counting mechanism.
However, the counting process was initially developed
without considering the possibility of using macro-diversity
techniques in ptm common channels, and MBMS users are
counted independently in each cell. Some extensions to this
counting process are proposed in this document as well as a
discussion about the criteria method used by this
mechanism.
We propose to analyze radio resource management
methods concerning the efficient usage of the current
UMTS radio resources for broadcast/multicast kind of
services.
MBMS counting should be used to decide whether the
identical MBMS service should be transmitted in a ptp
or ptm mode to a group of users. The proposed strategy
is based on the total transmit power in a cell.
Macro-diversity combining for ptm connections is
crucial for MBMS, as improving significantly the
received signal quality at the receiver and therefore
offering a substantial de-crease in transmit power. In a
multi-cell transmission, instead of avoiding
interference at the cell border, all the neighbouring
cells are used to transmit the same information
synchronously to the UE, which requires an extended
counting scheme.
As a final remark, a hybrid MBMS counting mechanism
based first on the number of UEs and then, if applicable, on
the instantaneous transmit power of both ptp and ptm
transmission modes should be considered for study. While
maintaining the same MBMS counting mechanism mode for
a large group of users, this may provide a more accurate
decision method being worthwhile in terms of radio resource
availability.
6) MBMS Cell Throughput EnhancementsResearch projects, such as C-MOBILE, have to
investigate how to increase the MBMS throughput. Forexample, it is proposed to specify the behaviour of UEs with
a dual receiver. These UEs will be able to receive
simultaneously dedicated services on one frequency and
MBMS services on the other frequency.
Cell throughput could also be investigated in terms of
efficient admission control mechanisms that would consider
QoS considerations including both service differentiation
and the bimodal nature of the cells (i.e., ptp or ptm).
Efficient Admission Control schemes will consider the se-
lected channels used and the handover specific requirements,
and can also be hybrid in nature to handle the change of cell
mode from ptp to ptm and vice versa, to achieve the bestpossible cell throughput.
7) Multicast Mobility SupportThe user shall be able to continue receiving MBMS
services throughout the MBMS service area in which the
service is provided. For example, in the case of handover
and assuming that a certain multicast service is offered in the
target cell, it should be possible for the user to continue the
session in the target cell. It is possible that data loss will
occur due to user mobility. If the service is not available in
the neighbouring cell towards the user is moving, he should
be informed of that. Research is needed to investigate how to
realize the handover and to propose improved RRM
schemes.
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
5/7
Page 5 (7)
5
8) Dynamic Feedback for MBMS Common ChannelsThe introduction of MBMS provides multimedia services
to a large number of subscribers. The main barrier is the
inability of FACH to deliver MBMS services efficiently to
its multicast groups. The proposed power control algorithm
aims at overcoming the shortfall of FACH by improving on
its power transmission efficiency. The traditional FACH was
not created to deliver multimedia services to UEs. FACH
must be recognized differently as a new common channel
together with the proposed power control algorithm, which
aims at efficiently reducing transmission power in order to
efficiently utilize the available band-width. MBMS
Optimized Transmission Schemes
9) Non-Uniform Hierarchical ModulationIn a wireless communication network, depending on the
link conditions in broadcast and multicast transmissions,
some receivers will experience a better signal-to-
interference-and-noise ratio (SINR) than others, and thus the
capacity of the communication link for these users is higher.
A very simple method to improve the efficiency of thenetwork is to use hierarchical signal constellations (also
called embedded or multi-resolution constellations) which
are able to provide unequal bit error protection. In this type
of constellations there are two or more classes of bits with
different error protection, to which different streams of
information can be mapped. Depending on the propagation
conditions, a given user can attempt to demodulate only the
more protected bits or also the other bits that carry the
additional information. By using non-uniformly spaced
signal points, it is possible to modify the different error
protection levels. Depending on the UE position in the cell,
the users will demodulate the received signals either as 64-QAM (being discussed for HSPA+), 16-QAM, or QPSK.
These techniques are interesting for applications where
the data being transmitted is scalable, and can be split in
classes of different importance. In the case of video
transmission, for example, the data from the video source
encoders may not be equally important. The same happens
in the transmission of coded voice.
10) QoS Differentiation & Multi-Resolution BroadcastSharing channels is one of the most important aspects in
network optimization.
In scalable media, a base layer can be provided to satisfy
minimum requirements, and one or more enhancement layers
can offer improved qualities at increasing bit/frame rates and
resolutions. This method significantly decreases the storage
costs of the content provider and enlarges the effective
MBMS coverage area.
Common scalability options are temporal scalability,
spatial scalability and SNR scalability. Spatial scalability
and SNR scalability are closely related, with the difference
of an increased spatial resolution provided by spatial
scalability.
SNR scalability implies the creation of multi rate bit
streams. It allows for the recovery of coding errors, or the
difference between an original picture and its reconstruction.
Spatial scalability allows for the creation of multi-resolution
bit streams to meet varying display requirements and
constraints for a wide range of clients. It is essentially the
same as SNR scalability, except that a spatial enhancement
layer here attempts to recover the coding loss between an
up-sampled version of the reconstructed reference layer
picture and a higher resolution version of the original
picture.
B. Repeating Strategies & Ad-hoc NetworksNew topological approaches like multi-hop solutions and
repeating allow for an increased coverage of high rate data
transmission. Repeating can provide path loss savings and
can take advantages of the spatial diversity and the broadcast
nature of wireless networks. This will also allow for
delivering high data rate multicast content like MBMS to
large and spatially distributed user groups. The relatively
small regions covered by repeaters allow for reduced
transmitting powers with accordingly reduced interference.
The objective of this activity is to increase coverage for
high data rate transmission by covering remote areas and to
enable high data rate transmission for nearby but shadowed
areas. This enhancement of the region with high data rate
reception could be realized stepwise and also temporarily by
installing repeaters at locations where there is a special need.
Repeaters can act as gap fillers for shadowed locations
(e.g. inside of buildings). It has to be investigated whether
repeater networks can benefit from macro-diversity.
Especially, this could be the case with OFDM.
Strategies and algorithms for adaptive repeating could
extend the high data rate coverage with minimal additional
interference. The repeaters in a communication system could
possibly be used to deploy cells with dynamically
configurable sizes and forms, allowing for adapting the cell
structure to the user distribution and demand for high data
rate services.
C. Exploitation of Location InformationAs mentioned above, efficient mechanisms to switch from
ptp to ptm and vice-versa should be researched. Positioning
information can further be used to guide the setup of a ptm
radio bearer to serve a group of users close to the base
station and a ptp bearer for a single user at the cell border.
In addition, the exploitation of location information
should be investigated to trigger a handover at optimal
positions so as to make the most use of the base station
transmit power when the UE is moving from a ptm cell to a
ptp cell and vice versa. This work item is fostered by the factthat mobile terminals are expected to support GPS (or
assisted GPS) in the future.
D. MBMS Mobility ManagementA further research topic is the examination of the
interaction of mobility procedures and MBMS to identify
and better understand major limitations and key issues that
may influence the performance of the MBMS feature, and to
anticipate eventual problems in its deployment. Concerning
interaction of MBMS support with existing mobility
procedures, it will be important from an operator point of
view (especially in an initial deployment phase) that areaswhere MBMS is deployed may coexist with areas where
MBMS is not yet available.
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
6/7
Page 6 (7)
6
E. Receiver Baseband EnhancementsResearch might consider but will not be limited to the
techniques presented below.
1) Interference CancellationThe use of interference cancellation schemes (here the
term interference is used in a broad sense, including
multiple-access interference, inter-symbol interference,
inter-antenna interference, etc.) allows significantperformance improvements in most cases.
Interference cancellation schemes can be implemented in
a linear or iterative way and eventually combined with
iterative channel decoding. Intelligent schemes that trade
receiver performance vs. complexity would be of particular
interest. In general, interference cancellation will be
beneficial for both WCDMA based systems and LTE.
2) UE Receive DiversityC-MOBILE will consider the performance of receive
diversity on MBMS as an option, in the course of
developing new features.3) Advanced Decision-Directed Channel Estimation
In wireless communications, the mobile propagation
conditions lead to channels that distort the amplitude and
phase of the transmitted signal. This distortion has to be
estimated and tracked when performing coherent detection
in the receiver. An alternative are systems employing non-
coherent detection, but this incurs significant performance
degradation. Therefore, most of the mobile communications
systems employ coherent detection and require that the
amplitude and phase distortions caused by the channel have
been correctly estimated. A common technique for obtaining
estimates of the channel response is the transmission of pilotsymbols along with the data. However, channel estimation
can be a complicated task due to:
the pilot symbols being severely affected by noise and
interference
the number of pilots in a frame being limited (to avoid
a substantial loss of data rate)
the power spent on the transmission of pilots being
kept at a low level
To compensate for these limitations, advanced receiver
configurations are suggested, based on the turbo-processing
concept. Channel estimation requirements are especially
higher for large non-uniform constellations and/or multi-antenna scenarios.
F. Transmitter Baseband Enhancements1) Advanced FEC Mechanism
In this working item, we may study the use of advanced
coding schemes for scalable media applications and
hierarchical coding and modulation. Raptor codes would be
an interesting option.
2) Macro Diversity & Soft CombiningIn the downlink, two main cases of macro-diversity can be
distinguished, depending on whether the base stations aresynchronized or not. In the synchronized case, the user can
employ a single receiver to demodulate the superimposed
signals. This makes it possible to realize a particular
structure known as Single Frequency Network (SFN). With
macro diversity, the diversity gain increases, but these
benefits are sensitive to temporal synchronisation. In fact, in
order to avoid interference between OFDM symbols, the
cyclic prefix is usually longer than or equal to the maximum
time spread of the multipath fading channel.
When the base stations cannot be assumed to be
synchronized, different receiver chains will be needed to
demodulate the signals from the distinct base stations. This
is still very complex. The technique of macro-diversity can
also be used by selecting the best cell base-station in terms
of the path-loss and shadowing (selection combining), in
order to further mitigate the adverse effects of interference.
3) Space-Time/Space-Frequency Coding &Beamforming
We can use multiple transmit/receive antennas to improve
the diversity. However, it is more interesting to use the
multiple antennas to increase the data rate, while maintaining
(or even improving) the power requirements. An issue that
has to be considered with these techniques is the increasedreceiver complexity and the fact that the correlation between
antennas should be relatively low.
Depending on the availability/quality of channel state
information (CSI) at the base station, the downlink data rate
can be improved by either open-loop or closed-loop spatial
multiplexing, in the form of Space-Time Coding (STC) or
transmit beamforming. In addition, OFDM-based systems as
discussed for LTE further allow for the use of Space-
Frequency Coding (SFC). While STC does not require
knowledge of the downlink CSI, beamforming can exploit
partial or full knowledge about the channel, in order to
improve the receiver SNR and therewith the data rate. Aninteresting solution is a hybrid scheme adapting to the CSI
quality.
While beamforming is well-studied for point-to-point
(ptp) links, fewer and quite recent results are available for
multicast beamforming on point-to-multipoint (ptm) links.
The differences are the following.
Typically, beamforming schemes for multicast are
designed in a way such as to maximize the minimum
receiver SNR among all users belonging to a certain
multicast group, in order to optimize for the minimum
achievable QoS. However, the group size plays an important
role in such an optimization.As it has been shown recently, the multicast capacity goes
to zero as the number of multicast user tends to be large. The
same argument applies to the special cases of multicast
beamforming and open-loop STC, where the latter does not
require transmit-side CSI and is, by construction, capable of
supporting multicast users.
Such as efficient ptp-ptm switching can help to improve
the total system throughput, also an advanced spatial
processing at the transmitter which adapts to the group size,
user location profile, and channel conditions of the multicast
users can be highly beneficial.
Although the multicast capacity which concentrates on theworst-case user goes to zero as the group size becomes
large, the good-case users could actually achieve a much
higher data rate and service quality. Non-uniform
-
7/30/2019 1- RAN Enhancements for Advanced MBMS
7/7
Page 7 (7)
7
hierarchical signal constellations are capable of adapting to
different channel conditions and providing different QoS
levels to the multicast users. Together with advanced spatial
processing at the transmitter, they are an effective means of
increasing the overall throughput.
4) Optimized Pilot InformationFor performing coherent detection at the receiver, it is
necessary that the amplitude and phase distortions caused bythe channel are correctly estimated. With this aim, pilot
symbols known by the receiver are usually transmitted along
with the data. The receiver performance will depend on the
channel estimation quality, which in turn depends indirectly
on the pilot structure. Therefore, several modes of pilot
transmissions together with advanced receiver
configurations (capable of enhanced channel estimation)
should be evaluated.
IV. CONCLUSION
Mobile broadcast services are attractive for mobile users and
offer new service opportunities for mobile operators. Inorder to efficiently support mobile broadcast services, 3GPP
has standardised Multimedia Broadcast Multicast Services in
UMTS Release 6. This paper identifies RAN enhancements
for MBMS support in current and future system. The C-
Mobile project investigates three reference systems. First,
systems based on WCDMA technology as they have been
already deployed or follow the evolution tracks in 3GPP.
Secondly, LTE (Long-Term Evolution) compatible systems
based on OFDMA and SC-FDE access technology will be
addressed. Finally, so-called future systems whose network
topology and access technology is open and that allow for
new concepts will also be studied. Research projects, such as
C-Mobile, are ensuring the evolutionary roadmap of MBMS.
REFERENCES
[1] M. Bakhuizen, U. Horn: Mobile Broadcast/Multi-cast in MobileNetworks, Ericsson White Paper, 2005
[2] R. Tnjes, U. Horn, F. Hartung: Business and TechnologyChallenges for Mobile Broadcast Services in 3G, 12th WWRF
Wireless World Research Forum, Toronto, 4-5 November, 2004.
[3] TS 23.246, Multimedia Broadcast/Multicast Service (MBMS);Architecture and functional description
[4] 3GPP TS 25.346 Introduction of the MBMS in the Radio AccessNetwork (RAN)
[5] C-MOBILE Deliverable D3.1 Research Directions and TechnologyRoadmap for RAN, June 2006.
[6] C-MOBILE Project Website: http://c-mobile.ptinovacao.pt/