Uplink Ground-based Beamforming with Multiplex
on Feeder Link and Fast Adaptive Algorithm for
Weights Optimization
Wei Shao, Hong Xue, Fanqiu Meng, Zuping Qian
College of Communication Engineering, PLAUST, Nanjing, China
Email: swlxssz@126.com
Abstract—The uplink ground-based beamforming (GBBF)
with multiplex on feeder link and fast adaptive algorithm for
weights optimization is studied in this paper. With the methods
of code division multiplex (CDM) and wavelet packet division
multiplex (WPDM) against the bottleneck problem on the limited
transformation bandwidth and the big number of channels on
feeder link, the spectral efficiency for feeder link can be
improved obviously. The CDM is applied to separate each
channel through orthogonal spreading sequences and improve
the spectral efficiency up to multiple times. With orthogonal sub-
carriers lapped in frequency domain, the WPDM has a higher
spectral efficiency than the frequency division multiplex (FDM).
Different from the least mean squares (LMS) algorithm, the
constrained stability least mean squares (CS-LMS) algorithm
provides a weights optimization recursive formula with adaptive
step size updated automatically according to the signal
transformation environment. As a result, with the CS-LMS
algorithm, a faster convergence rate can be obtained especially
under strong interference or time-varying environment, such as
some satellite mobile communication scenarios. Simulation
experiments shows, the uplink GBBF with multiplex on feeder
link and fast adaptive algorithm for weights optimization leads to
high spectral efficiency and good convergence performance.
Index Terms—Ground-based beamforming, code division
multiplex, wavelet packet division multiplex, constrained
stability least mean squares.
I. INTRODUCTION
With the increasingly growth of the public communication
service requirement, many realistic issues appear, such as the
coverage difficulty of communication network in remote and
sparsely populated regions, and the emergency measures lack
at the time of natural disaster like earthquake. With the goal of
ubiquitous coverage, the hybrid satellite-terrestrial mobile
communication system, which is very attractive in recent years,
can realize a seamless connectivity between the satellite and
the terrestrial mobile communication network [1, 2, 3]. The
structure of the system is shown in Fig. 1, in which the
terrestrial communication network is called ancillary terrestrial
network (ATN) and the terrestrial mobile terminal is called
ancillary terrestrial components (ATC). A same frequency
band is shared between satellite and ATC base station.
Moreover, the air interface format is also almost same. The
mobile terminals shift between ATN and satellite network
automatically.
ATC
PSTN, GSM,
CDMA
Gateway
Network
Control
Center
Forward
Uplink
Reverse
Downlink
Forward
Downlink
Reverse
Uplink
User Terminal
Satellite
Fig. 1. The hybrid satellite-terrestrial mobile communication system
Beamforming is implemented by adjusting the amplitude
and phase of each signal path routed to each feed element.
Each individual signal path is routed to multiple feeds with
relative amplitudes and phases which define each intended
beam. Recent mobile satellite programs have employed an
onboard digital signal processor (DSP) which performs digital
beam forming (DBF) allowing an entire beam pattern to be re-
optimized at any time during the life of the spacecraft. Via
onboard beamforming, the anti-jamming and anti-interception
performances are also improved. However, the significant
complexity of power, weight, cost and signal processing will
also be added to payload.
Therefore, it’s necessary to study the ground-based
beamforming (GBBF) technology transferring all or part of
beamforming tusks from satellite to gateway on earth to
provide the same or greater flexibility than DBF onboard the
satellite without the penalty of an onboard DSP.
However, the number of feed link space dimensions
becomes very big due to the great number of array elements
onboard, e.g., one hundred or so. As a traditional feed link
signal multiplex method, most satellite feeder link requiring
multiple paths employ frequency division multiplex (FDM)
whereby each path is transferred between the ground station
and the satellite on a separate frequency. As a result, the total
available bandwidth of feeder link is not enough for the total
required transformation bandwidth for FDM, which can be
605
978-1-4799-8897-6/15/$31.00
c
2015 IEEE