• Journal of KIISE:Information Networking
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• v.35 no.2
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• pp.149-157
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• 2008

Since wireless sensor networks consist of nodes with the constrained battery, energy efficient MAC operation is one of the important issues. Low duty cycle operation is critical to conserve energy in wireless sensor network MAC protocol. Some paper proposed a new approach to low power listening, which employs a short preamble to further reduce energy consumption and to reduce latency. But short preamble suffers from unfair channel access problem since there was no consideration for contention between transmission nodes. Preamble counting proposes a solution to each of these problems by employing node selection information. Simulation results show that the preamble counting provides an improved energy efficiency and fairness of packet delivery.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.204-209
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• 2010

Idle listening is very critical source of energy dissipation in wireless sensor networks. To reduce idle listening, we propose preamble sampling MAC that is named EESP-MAC. The main idea of EESP-MAC is to add control information into the short preamble frame. So the stream of short preambles is used not only for preamble sampling but also for avoiding overhearing, decreasing control packet overhead and reducing the listening of the redundant message, caused by message-flooding.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5A
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• pp.502-513
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• 2004

This paper proposes a symbol synchronization method in the IEEE 802.11a wireless OPDM system, which uses only signs of the in-phase and the quadrature signals in the short preamble. The short preamble is sampled with 2 tines of Nyquist sampling rate and both of the autocorrelation and the cross-relation are used in the proposed method. This method has some advantages that the ACG (Automatic Gain Control) can be processed concurrently during the short preamble and its implementation is not much complicated. The proposed symbol synchronization method is verified through simulations on frequency offset, multi-path and white Gaussian noise.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1725-1731
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• 2010

In this paper, we proposed preamble structure and code acquisition method to improve code acquisition performance for DS-SS/TDMA packet communication systems. Proposed algorithm changes the short PN code position depending on the sub slot number. Proposed algorithm also saves position differences between short PN codes and position offsets between short PN codes and data starting position of the TDMA packet. By using the position difference table, proposed algorithm can find out exact data starting position even though some sub slots were defected. As a result of simulation, we concluded that proposed algorithm has at least 5dB gain compared to conventional method when same short PN code is used. Moreover, proposed algorithm shows same code acquisition performance only with 1/4 shortened short PN code compared to conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1436-1444
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• 2000

In this paper, we propose the joint carrier and symbol timing recovery algorithm using repetitive preamble and differential detection for burst modem. The proposed algorithm can estimate the frequency offset and the symbol timing error regardless of the amount of frequency offset, with a high accuracy, even using very short preamble and at low SNR values. The algorithms for continuous phase frequency shift keying (CPFSK) and phase shift keying (PSK) types are developed. Through computer simulations, we compare the proposed algorithm with the existing algorithms on the estimation accuracy in terms of the preamble length, and analyze those bit error rate(BER) performance.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.1
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• pp.70-77
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• 2008

On the wireless sensor network MAC protocols, one of main issues is energy enciency. Since several asynchronous wireless sensor network MAC protocols with short preamble sampling scheme can be operated without setting the timing synchronization among neighbor nodes, it consumes a little energy for maintaining protocols. However, each node encounters either preamble or data overhearing problem, because each node wakes up in a different time and must check whether the frame is being sent to itself or not. To solve this overhearing problem, we newly propose B-MAC++ that can reduce the overhearing energy consumption by using short preambles with destination address and payload length. from simulation results, we show that the proposed B-MAC++ has advantageous in terms of power consumption efficiency over other asynchronous wireless sensor network MAC protocols.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2638-2647
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• 2010

X-MAC reduces transmission delay and energy consumption by using a short preamble instead of the existing long preamble. To solve the problem of X-MAC, this paper proposes a new MAC protocol called Express-MAC. The wireless sensor network is mainly used for the purpose of gathering event data or situation information. Especially, the transmission pattern of the sensor network with the purpose of event detection such as intrusion detection is very intermittent as well as successively occurring when a single event takes place in most cases. By reflecting sensor network's key transmission patterns as above, EX-MAC has used multi-hub path's path reservation system and awake section's transmission time reservation method in data transmission when the first event takes place. The awake time reservation in transmission path has improved successive data transmission's end-to-end delay, and it has also increased efficiency in terms of energy consumption by reducing the preamble length of data transmission and reception node.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.1
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• pp.43-49
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• 2014

This paper proposes an optimized multi-bit digital FSK receiver robust to large carrier frequency offset (CFO) toward recently emerging long-range WPAN standards. Due to a short preamble length and strict BER requirements, we design a simple multi-bit digital demodulator combined with CFO estimator which guarantees the target BER performance. Simulation results verify that the proposed FSK receiver achieves CFO-free BER performance with the short preamble and satisfies the BER requirement by the recent WPAN applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.794-806
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• 2004

This paper deals with correction of frequency offset and analysis of quantization angle noise in the IEEE 802.1la OFDM system. The rotation phase per symbol due to the carrier frequency offset is estimated from auto-correlation of the short Preambles, which are over-sampled for the reduction of noise in OFDM signals. The pilot signals are introduced to estimate the rotation phase per OFDM symbol due to estimation error of the carrier frequency offset and the sampling frequency onset. During the estimation and correction of the frequency onsets, a CORDIC processor and a look-up table are used for the conversion between a rotation phase and its complex number. Being calculated by a limited number of bits in the CORDIC processor and the look-up table, the rotation phase and its complex number have quantization angle errors. The quantization errors are analyzed as SNR (signal to noise ratio) due to the quantization bit numbers. The minimum bit number is suggested to meet the specification of IEEE 802.1la properly. Finally, the quantization errors are evaluated through simulations on number of quantization bits and SNR of received signals.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.8-12
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• 2007

In this paper, we proposed an frequency offset estimation scheme which can be used for packet based OFDM communication systems such as IEEE802.11a and IEEE802.11p physical layer. Proposed estimation scheme can adjust the gain allocation ratio between long training symbol and short training symbol while maintaining average power of overall training sequence so that we can obtain the reference parameters for MSE performance improvement. The preamble structure considered in this paper is based on the preamble specified in IEEE802.11a and IEEE802.11p standardization group. From the simulation results, it is shown that power ratio between long training symbol and short training symbol must vanes for achieving lower frequency offset estimation error as channel SNR condition is changed. Also it is known oat proposed scheme can achieve better performance than conventional one.