Dr. Tripathi, a Principal
Consultant at Award Solutions, joined Award Solutions in March 2004, bringing
his knowledge and experience in mobile wireless technologies to facilitate the
planning, development and delivery of technical training seminars. He teaches and consults on various
technologies including, LTE E-UTRAN and EPC, WiMAX, UMTS R99, HSDPA, HSUPA,
HSPA+, 1xEV-DO, IMS, and WiMAX. He has
taught various aspects of 3G and 4G commercial cellular technologies including
but not limited to network operations, network planning, and network
Since receiving his doctorate in
Wireless Communications from Virginia Tech, Dr. Tripathi has held several
strategic positions in the wireless arena.
For Nortel Networks, he worked to analyze and optimize the performance
of CDMA networks, in such areas as load balancing, handoff, power control,
supplemental channel management, and switch antenna diversity. As a Senior
Systems Engineer and Product Manager for Huawei Technologies, Dr. Tripathi
worked on the infrastructure design and optimization of CDMA2000, 1xEV-DO, and
UMTS radio networks. He has significant experience designing, analyzing, and
field-testing Radio Resource Management algorithms for CDMA2000 and 1xEV-DO.
In 2001, he co-authored a book on
Radio Resource Management, and he is the author of numerous research papers and
patent submissions. He has contributed
chapters to two books on applications of fuzzy logic to communications and
applicability of network neutrality principles to wireless systems. He is a co-author of an upcoming book on
cellular communications (to be published by IEEE/Wiley).
Tripathi's position at Award Solutions puts him at the forefront of emerging
technologies. He has authored courseware
related to LTE, WiMAX, 1xEV-DO, HSUPA, UMTS optimization, 1xEV-DO RF
optimization, advanced antenna techniques, and IP convergence. In addition to teaching the students in the
Industry, he also trains his colleagues (i.e., instructors) on various
technologies (e.g., LTE, WiMAX, 1xEV-DO, HSDPA, HSUPA, 802.11n, and advanced
antenna techniques). His extensive
knowledge, hands-on experience with commercial deployments, and enthusiasm for
the subject matter, coupled with a passion for teaching, provide the foundation
for consistently enjoyable, informative, and effective classes.
For those who are too picky on the definition of "true 4G,"
hold your breath...4G version of LTE is taking shape as LTE-Advanced! LTE-Advanced is a Release 10 feature of 3GPP. Recall that Release 8 defined LTE. Release 9 makes some enhancements to LTE such
as support for emergency calls using IMS. We'll summarize below motivating
factors behind LTE-Advanced and briefly introduce main features of LTE-Advanced.
ITU (International Telecommunication Union) has defined
requirements for IMT-Advanced (just a prettier name for 4G?). LTE-Advanced aims to meet and often exceed
IMT-Advanced requirements. Remember that
LTE is a Lon...g Tem Employment (LTE!).
Hence, LTE-Advanced needs to aim for an even longer term employment! IMT-Advanced requires the support for 100 Mbps
for high mobility and 1 Gbps for low mobility.
While Release 8 can already meet 100 Mbps peak rate requirement,
enhancements are needed in Release 10 to support 1 Gbps. Peak spectral efficiency targets in
IMT-Advanced are 15 bps/Hz and 6.75 bps/Hz for DL (downlink) and UL (uplink),
respectively. LTE-Advanced aims to
achieve the peak spectral efficiency of 30 bps/Hz and 15 bps/Hz in DL and UL,
respectively. IMT-Advanced needs to support
wider bandwidths such as 40 or 100 MHz.
LTE-Advanced allows 100 MHz bandwidth.
While IMT-Advanced specifies the delay of 100 ms for an idle mode to
connected mode transition, LTE-Advanced intends to achieve a 50 ms delay. Recall that even Release 8 LTE can meet the
100 ms transition delay requirement. In
addition to IMT-Advanced requirements, LTE-Advanced attempts to achieve higher
performance with reduced cost.
Furthermore, LTE-Advanced facilitates meeting future operator and user
needs. Note that wireless data traffic
has been experiencing explosive growth. Of
course, LTE-Advanced cannot forget the competition...LTE-Advanced needs to be
prepared for its arch rival- WiMAX! In
summary, IMT-Advanced requirements, lower cost per bit, and competition are
major motivating factors driving the design of LTE-Advanced.
Let's turn our attention to the main features of
LTE-Advanced. LTE-Advanced is primarily
an air interface enhancement, and, hence the features that we would briefly
highlight below are related to the radio link between the UE and the
eNodeB. Main features of LTE-Advanced
are Carrier Aggregation, DL MIMO enhancements, UL SU-MIMO, CoMP (Coordinated
Multipoint), and Relay. Main benefits of
these features are higher peak and average cell and user throughput and lower
cost per bit.
Carrier Aggregation means that multiple carrier frequencies
are aggregated to increase the overall bandwidth and hence data rates. These carrier frequencies are called
component carriers (CCs). The component
carriers may or may not be contiguous in frequency domain. A CC could have any of the channel bandwidths
defined for Release 8, which ranges from 1.4 MHz to 20 MHz. The eNodeB and the UEs may be capable of
transmitting/receiving one or more CCs.
The standard aims to support the total channel bandwidth of up to 100
MHz. Depending upon the UE capabilities,
the eNodeB may allocate multiple CCs to the UE for the DL and the UL.
While Release 8 already supports (4x4) DL SU-MIMO,
LTE-Advanced further increases it to (8x8) SU-MIMO in the downlink. Additionally, beamforming is enhanced in the
downlink using enhanced reference signals to improve MU-MIMO performance. Release 8 does not support SU-MIMO in the
uplink. However, Release 10 extends
SU-MIMO to the UL with the support for up to four layers of spatial
If you were missing soft handoff/handover and fast cell (or
sector) switching in LTE, we have good news for you! CoMP introduced by LTE-Advanced works
similar to soft handover/handoff. CoMP
feature is available for the DL and the UL.
In the DL, it is CoMP Transmission, while it is CoMP reception in the
UL. Multiple cells could now be involved
in communication with the UE. Two main
CoMP transmission approaches are Joint Processing (JP) and coordinated
scheduling and beamforming (CS/BF). The JP
transmission approach offers two methods: (i) The eNodeBs transmit the same
information from two cells in the "joint transmission" method. The UE then combines these two signals
similar to a UMTS UE combining signals in soft handover. (ii) In the "dynamic cell selection" method,
one cell among a set of cells is dynamically chosen for the DL transmission to
the UE. In the CS/BF approach of CoMP
transmission, beams are formed in individual cells while reusing the
subcarriers near cell edge. Scheduling
in different cells would need coordination to realize such beamforming. The CoMP reception in the UL involves
reception of the UE signal at more than one cells. One of the cells would be a "central" cell
responsible to combine signals received at multiple cells.
A relay can be thought of as an enhanced repeater, where the
cell coverage (and hence cell-edge throughput) can be extended/improved. A new interface, Un interface, exists between
the traditional eNodeB and a relay node.
An example of relaying in LTE-Advanced is Layer 3 relaying with self
backhauling. The eNodeB uses the help of
a relay node that takes care of some users.
Such users would be outside the coverage area of the eNodeB but inside
the coverage area of the relay node.
LTE-based air interface can indeed be used as the wireless backhaul
between the eNodeB and the relay node.
Such backhaul could share the same bandwidth with users or could use
different spectrum bandwidth.
LTE-Advanced is fully backward-compatible with Release 8
LTE. A Release 8 UE can work with a
Release 10 E-UTRAN, and a Release 10 UE can work with a Release 8 E-UTRAN. LTE-Advanced would support interworking with
legacy technologies such as UMTS and 1xEV-DO.
We hope that you have digested LTE-Advanced in 5 minutes. If you finished up digesting LTE-Advanced in
less than 5 minutes, congratulations! If
you took longer than 5 minutes, well...what can we say...you are a slow reader and
you need to work on your reading skills!
"See" you next time!