Rebirth: Starting from Lighting Up the Tech Tree

Chapter 18 72 Hours

Before the final, Zuo Cheng must first win the tough battle of stage two.

The problem of porting the algorithm to the custom chip has been solved. The next step is system integration and joint debugging—installing the ported algorithm into the signal processing unit of the Blue Bay Communication South District experimental base station and connecting it with other modules of the base station to ensure that the whole system can operate in coordination.

Han Zhe granted Zuo Cheng remote access, but the final step of the joint debugging phase had to be done on-site—because the radio frequency module and antenna array of a real base station could not be simulated remotely, and the end-to-end test of the signal link had to be run on physical equipment.

On November 8th, Zuo Cheng and Fang Ze went to the Lanwan Communication South District base station together.

The base station was built on the roof of a commercial building. Outside was a row of white antenna arrays, and inside was an equipment room of less than 20 square meters, crammed with cabinets, fiber optic cables and cooling fans. The buzzing noise was so loud that you had to raise your voice to speak.

Lanwan Communications sent a field engineer to assist them. His name was Lao Wu, and he was in his forties. He was wearing an oil-stained work uniform and spoke with a heavy southern accent.

"You two are from the school?" Old Wu looked them up and down, his tone tinged with well-meaning skepticism. "So young, are you sure you can handle this?"

"You'll know once you try it." Zuo Cheng smiled and opened the debug port of his laptop to connect to the base station.

The first half of the integration test went unexpectedly smoothly. The algorithm module and the base station's baseband processing unit successfully connected, the data path was working, and signal acquisition and output were normal. Fang Ze monitored the embedded platform's operation throughout, and memory usage, CPU load, and interrupt response time were all within safe limits.

The problem lies in the radio frequency (RF) end.

When Zuo Cheng switched the algorithm to real-time processing mode and started receiving real wireless signals from the antenna array, the output data exhibited a strange periodic jitter—every four seconds or so, the channel estimate would suddenly shift once and then return to normal.

The deviation was small, but enough to cause the performance metrics to drop below the benchmark.

"This jitter isn't an algorithm problem." Fang Ze frowned, looking at the waveform on the oscilloscope. "The period is too regular, once every four seconds; it sounds like external interference."

Zuo Cheng also noticed this pattern. He turned to Lao Wu: "Are there any devices around the base station that generate electromagnetic interference with a four-second cycle?"

Old Wu thought for a moment, then slapped his thigh: "There's a weather monitoring station on the roof of the building next door, and the radar on it rotates once every four seconds. Engineers have raised this issue before, but because it doesn't affect regular communications, it hasn't been addressed."

Zuo Cheng and Fang Ze exchanged a glance.

The sidelobe signal of the weather radar leaked into the base station's receiving frequency band, causing interference with each rotation. Conventional communication algorithms are not sensitive to this level of interference, but Zuo Cheng's adaptive tracking algorithm, with its higher accuracy, actually "saw" this interference.

Too much precision can also be a problem.

"Two paths." Zuo Cheng quickly drew a diagram on his notebook. "The first path is to add a notch filter to the front end of the algorithm to directly filter out the frequency band of the weather radar. It's simple and crude, but it will lose a small segment of useful spectrum. The second path is to add a periodic interference identification mechanism to the adaptive tracking module, allowing the algorithm to learn to distinguish between radar interference and useful signals."

"The second one is more elegant, but the development time is longer—" Fang Ze said.

"Two hours is enough," Zuo Cheng said.

Fang Ze glanced at him, did not question him, and turned to open a new branch in the debugging environment.

Zuo Cheng sat down to write code. The logic for identifying periodic interference is not complicated—the frequency, amplitude, and duration of the interference are fixed. As long as a pattern matching layer is added to the input of the tracking module, the interference characteristics can be identified and stripped from the signal, leaving only the clean and useful signal.

An hour and a half later, the new module was finished. Fang Ze flashed the code into the chip and ran the test again.

The four-second jitter disappeared. The channel estimation curve became smooth and stable, and all performance metrics returned to above the acceptable level.

Old Wu watched the whole thing from the sidelines. The doubt that had been on his face was long gone, replaced by the satisfaction unique to an old engineer.

"You guys are pretty good." He patted Zuo Cheng on the shoulder, the force so strong that Zuo Cheng staggered forward half a step. "This radar interference problem has been bothering us for half a year, and you solved it in just one afternoon."

"It was just a matter of convenience." Zuo Cheng steadied himself and smiled.

The joint testing is complete.

The final hurdle is the 72-hour continuous operation verification.

The algorithm must run continuously for three days and three nights in a real base station environment, processing the communication signals of thousands of real users, without any crashes, freezes, or performance drops during this period.

At 10:00 AM on November 10th, Zuocheng launched a 72-hour test.

The first twenty-four hours were uneventful. The algorithm ran stably, with all indicators above the target and minimal fluctuations. Zuo Cheng checked the running status remotely every two hours, while Fang Ze monitored the resource consumption of the embedded platform in real time.

At 4 a.m., in the thirty-sixth hour, Zuo Cheng was awakened by his phone vibrating.

Fang Ze sent a message: "Memory leak. It's very slow, increasing by about 0.3% per hour, but if this continues, it's expected to hit the limit around the sixtieth hour."

Zuo Cheng sat up abruptly, turned on his computer, and remotely connected to the base station to debug the system.

Fang Ze is right. The memory usage of the embedded platform is increasing at an extremely slow rate—0.3% per hour, which is imperceptible in the short term, but over 72 hours that's more than 20% growth. Once the memory is full, the system will either slow down or crash.

"Located." Fang Ze sent another message at 4:20 AM. "The interference detection module's buffer isn't being dynamically overwritten. Each time interference is detected, a small block of new memory is allocated to record a log, but it's not released after recording. This isn't noticeable in short-term tests, but it accumulates over long periods."

Zuo Cheng closed his eyes for a second.

This is a bug in his own code. The module was rushed out in an hour and a half, and the testing was insufficient, resulting in a missed memory release.

"Can you hotfix it?" he asked. Hotfix refers to patching the system online without restarting—if a restart is necessary, the 72-hour test timer has to start all over again.

Fang Ze replied with two words: "Yes. But you need to remotely compile the patch package here, and then I'll push it."

Zuo Cheng spent fifteen minutes writing the patch—changing the buffer to a circular structure of fixed size, where new data automatically overwrites the oldest data, keeping memory usage constant. Fang Ze pushed the patch remotely, and the hotfix was successful.

The memory usage curve immediately flattened out.

At 4:42 a.m., everything returned to normal.

Zuo Cheng leaned back in his chair, his back covered in cold sweat.

If Fang Ze hadn't discovered the problem at 4 AM, and had waited until the memory crashed at the 60th hour to address it, the 72-hour test would have been wasted, and the deadline for stage two would have become extremely tight.

He sent Fang Ze a message: "Thanks. This bug is my fault."

Fang Ze replied, "Everyone who writes code will have bugs; the important thing is to find them early. Go to sleep; I'll keep an eye on things later."

Zuo Cheng didn't sleep anymore. He sat in his dark dormitory, staring at the slowly fluctuating data on his computer screen, until dawn.

The seventy-second hour.

10:00 AM on November 13th.

Zuo Cheng, Fang Ze, and Lao Wu stood in the base station equipment room, staring at the final report on the monitoring screen.

连续运行72小时。处理用户信号总量：4,217,603条。信道估计平均精度：超出基準值34.2%。系统崩溃次数：0。性能骤降次数：0。内存泄漏：已修复，修复后运行36小时无异常。

Old Wu took a sip of the strong tea in his thermos and nodded: "Passed. Passed perfectly."

Zuo Cheng looked at the numbers on the screen, said nothing, and just let out a long sigh.

The light screen lit up in my consciousness:

[Main Quest Chain - Breaking the Communication Impasse - Part Two: Completed!]

[Actual Test Verification Evaluation: Excellent (0 crashes in 72 hours, performance exceeds target by 34.2%)]

[Rewards are being distributed]

[Unlocking the Blades: Communication Systems Engineering ✓]

[Points +10 (Current Points: 23)]

[Due to the "Excellent" evaluation rating, the deadline for stage three has been extended by an additional 7 days.]

[Part Three is about to be unlocked—]

Twenty-three points. Five leaves.

Zuo Cheng turned off the control panel and glanced at Fang Ze. Fang Ze leaned against the server rack, hands in his pockets, expressionless, but with a very slight smile at the corner of his mouth.

"Let's go," Zuo Cheng said. "Back to school. The finals are in four days."