We have proposed an intracell uplink of a spread-spectrum code-division multiple-access (SS-CDMA) flexible wireless network based on approximately synchronized (AS) CDMA. Since the AS-CDMA has no co-channel interference, complicated transmission power control (TPC) is not required. A modem of the AS-CDMA has been designed and implemented for the Japanese 2.4 GHz industrial, scientific and medical (ISM) band. Using the implemented modem, the degradation of Eb/N0 from the theoretical limit is 1.0 dB at a bit error rate (BER) of 10-3. Under 2-user environment, the degradation of carrier-to-noise ratio (CNR) is 0.5 dB at a BER of 10-3 when the desired-to-undesired signal ratio (DUR) is -20.3 dB. We have evaluated BER performances in cases of varying carrier frequency offset and median DUR with computer simulation. Under 8-user environment, at the carrier frequency offset of 0.3 ppm, the BER with the DUR of -16 dB is found to be 10-3. Using the AS-CDMA with a 4-step open-loop TPC technique, the design of intracell uplink is available.

An asynchronous spread spectrum (SS) modem for 2.4-GHz wireless LAN has been implemented using an efficient ZnO-SiO2-Si surface acoustic wave (SAW) convolver. The design of the highly efficient SAW convolver was developed at Tohoku University and commercially manufactured by Clarion Co., Japan. The modem can operate under full-duplex transmission in the same frequency range of the 2.4-GHz SS band. The SS modem is based on a direct-sequence/code-shift-keying (DS/CSK) method for the modulation. Pseudo-noise (PN) codes are chosen from a preferred pair of 127-chip m-sequences and the code rate is 14MHz. The asynchronous demodulation is simply realized utilizing the coherent correlation characteristics of the SAW convolver. Under full-duplex transmission, the self-jamming caused by a transmitted signal in the modem itself is effectively reduced by an RF isolator and the SS processing gain. The implemented modem has been tested using a coaxial cable with attenuator. A bit error rate of 10-6 under full-duplex transmission is observed at 78.3dB of a desired to undesired signal ratio. The effective range is estimated on the basis of two-path propagation model. From self-jamming rejection of 78.3dB, the effective range under real-time full-duplex is estimated to be about 200m.

An asynchronous spread spectrum (SS) wireless modem has been implemented using an efficient ZnO-SiO2-Si surface acoustic wave (SAW) convolver. The modem is based on a direct-sequence/frequency-shift-keying (DS/FSK) method for the modulation. The demodulation is carried out asynchronously utilizing the coherent correlation characteristics of the SAW convolver. In order to improve the narrowband interference rejection capability, we propose a new technique based on the reference signal control. A notched-reference-signal circuit and a self-convolution canceler are implemented in the SS modem for the reference signal control. It was found that the antijam capability for narrowband interference is at least -24dB of desired-to-undesired power ratio (D/U); the improvement of the antijam capability is 16dB up as compared with our previous SS modem.

We have proposed a current-cut switched-current matched filter (CC-SIMF) for direct-sequence code-division multiple-access (DS-CDMA). The 256-chip CC-SIMF can achieve low power consumption of less than 10 mW under high-speed operation of more than 16 Mcps. To reduce the current transfer error accumulation, we propose a parallel SIMF configuration. A 128-chip SIMF using 0.8-µm Complementally Metal Oxide Semiconductor (CMOS) process has been designed and fabricated. Optimization of the current memory cell structure has been described. The correlation operation at 16 Mcps has been obtained using a 128-chip orthogonal m-sequence. The code phase separation performance for path diversity has been clearly observed. The power consumption has been significantly reduced using the current-cut method.

In the present GHz-clock high-density LSI, a design of signal lines is getting so critical that the transmission line analysis should be introduced to signal line design. This leads to the complex design of line structure and i/o drivers including impedance matching. Our target is to implement a system-in-package (SiP) for software-defined-radio (SDR). The SiP operates up to 10 GHz, and requires a compact and high-density packaging technology with a simple signal wiring design. In this paper, we propose a new concept of 3-D multilayer-stacked SiP. The new 3-D packaging concept includes (1) design guideline for interconnection lengths, (2) bridging register circuits in LSI chips, (3) flip-chip microbump bonding technology of chips onto system-buildup printed wiring boards (PWB), (4) multilayer-stacked 3-D package of several sets of chips and PWB, and (5) 100-µm-diameter bumps at peripheral region of PWB as vertical via-bump bus lines. A critical interconnect length, in which interconnect wiring is treated as a conventional RC line, is discussed for wiring design. Both wiring lengths in LSI chips and that among chips corresponding to total thickness of vertical bus lines are designed to be shorter than the critical length. The key points of the 3-D package for GHz signal transfer are a delay guarantee due to limitation of line length and separation between local lines in a chip and a bus line among chips.

We have proposed and implemented a spread spectrum (SS) wireless switch using 2.4 GHz front-end AlN/Al2O3 surface acoustic wave (SAW) matched filter (MF). Since the SAW MF has radio frequency (RF) front-end operation, RF components are not needed in the received circuit. High impedance in the peripheral circuit using passive devices has been employed for low current consumption. The SS wireless switches have been designed with the power consumption of less than 100 µW by using the SAW MF. It is confirmed that implemented SS wireless switch has a long battery life of 10 years and communication range of 30 m.

We have proposed the packet SS-CDMA scheme for downlink of SS-CDMA flexible wireless cellular network. Transmission packet is framed with synchronization block with 11 chip Barker code and information block with orthogonal spreading code. The chip synchronization is carried out using short code surface acoustic wave (SAW) matched filter. The code de-spreading is carried out using in-line de-spreader. Multi-channel downlink of 63 channels can be designed using orthogonal m-sequence. Simulation results show more than 15 channels without degradation from theoretical value can be used under multi-path environment. The packet SS-CDMA modem has been implemented using a 2.4 GHz front-end SAW matched filter. Degradation of Eb/N0 of less than 0.5 dB is experimentally achieved with four-channel multiplex.

Two error control schemes for Transmission Control Protocol (TCP) connection on a wireless network are proposed that can minimize the degradation in radio link throughput due to retransmission. One scheme is based on the discard of TCP retransmission packets, and the other is based on the suppression of transmission delay fluctuation. Simulation results show that the degradation in throughput is reduced by 7.2% by using each proposal scheme when the frame error rate is 10e-3.